diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 4373ec6..ea9da33 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -6,21 +6,9 @@ updates:
       interval: weekly
     target-branch: main
     open-pull-requests-limit: 10
-  - package-ecosystem: maven
-    directory: "/"
-    schedule:
-      interval: weekly
-    target-branch: master
-    open-pull-requests-limit: 10
   - package-ecosystem: github-actions
     directory: "/"
     schedule:
       interval: weekly
     target-branch: main
     open-pull-requests-limit: 10
-  - package-ecosystem: github-actions
-    directory: "/"
-    schedule:
-      interval: weekly
-    target-branch: master
-    open-pull-requests-limit: 10
diff --git a/src/main/java/algorithms/sprint4/Map.java b/src/main/java/algorithms/sprint4/Map.java
index da9637b..3c156e9 100644
--- a/src/main/java/algorithms/sprint4/Map.java
+++ b/src/main/java/algorithms/sprint4/Map.java
@@ -137,7 +137,7 @@ static class Reader {
         private int len = 0;
 
         int read() throws IOException {
-            if (ptr == len) {
+            if (ptr >= len) {
                 len = in.read(buffer);
                 ptr = 0;
                 if (len == -1) {
@@ -189,6 +189,9 @@ int nextInt(int min, int max) throws IOException {
         char nextCommand() throws IOException {
             int c = read();
             while (c <= ' ') {
+                if (c == -1) {
+                    throw new IOException("Unexpected end of input");
+                }
                 c = read();
             }
 
diff --git a/src/main/java/kyu4/MorseCodeDecoder.java b/src/main/java/kyu4/MorseCodeDecoder.java
index cf6bb3e..56bd3c7 100644
--- a/src/main/java/kyu4/MorseCodeDecoder.java
+++ b/src/main/java/kyu4/MorseCodeDecoder.java
@@ -56,8 +56,6 @@ public class MorseCodeDecoder {
         ALPHABET_TO_MORSE.put("0", "-----");
         ALPHABET_TO_MORSE.put(" ", "   ");
 
-        MORSE_TO_ALPHABET.put("a", "b");
-        MORSE_TO_ALPHABET.put("c", "d");
         MORSE_TO_ALPHABET.put("-.-.-.", ";");
         MORSE_TO_ALPHABET.put("-...-", "=");
         MORSE_TO_ALPHABET.put("---", "O");
@@ -84,7 +82,7 @@ public class MorseCodeDecoder {
         MORSE_TO_ALPHABET.put("-.", "N");
         MORSE_TO_ALPHABET.put("..---", "2");
         MORSE_TO_ALPHABET.put("-....", "6");
-        MORSE_TO_ALPHABET.put("---...", ";");
+        MORSE_TO_ALPHABET.put("---...", ":");
         MORSE_TO_ALPHABET.put(".-.-.", "+");
         MORSE_TO_ALPHABET.put(".--.-.", "@");
         MORSE_TO_ALPHABET.put("....-", "4");
diff --git a/src/main/java/kyu6/GiveMeDiamond.java b/src/main/java/kyu6/GiveMeDiamond.java
index 7d9e02d..ce0ee3c 100644
--- a/src/main/java/kyu6/GiveMeDiamond.java
+++ b/src/main/java/kyu6/GiveMeDiamond.java
@@ -11,10 +11,10 @@ public static String print(int n) {
         int count = n / 2 + 1;
         StringBuilder strings = new StringBuilder();
         for (int i = 1; i <= count; i++) {
-            strings.append(" ".repeat(count - i)).append("*".repeat(i * 2 - 1)).append(System.lineSeparator());
+            strings.append(" ".repeat(count - i)).append("*".repeat(i * 2 - 1)).append('\n');
         }
         for (int i = count - 1; i >= 1; i--) {
-            strings.append(" ".repeat(count - i)).append("*".repeat(i * 2 - 1)).append(System.lineSeparator());
+            strings.append(" ".repeat(count - i)).append("*".repeat(i * 2 - 1)).append('\n');
         }
         return strings.toString();
     }
diff --git a/src/main/java/kyu6/Prime.java b/src/main/java/kyu6/Prime.java
index 3370936..4c1d010 100644
--- a/src/main/java/kyu6/Prime.java
+++ b/src/main/java/kyu6/Prime.java
@@ -1,15 +1,24 @@
 package kyu6;
 
 
-import java.math.BigInteger;
-
 
 public class Prime {
 
     //6 https://www.codewars.com/kata/5262119038c0985a5b00029f/train/java
 
     public static boolean isPrime(int num) {
-        return num > 0 && BigInteger.valueOf(num).isProbablePrime((int) Math.log(num) + 1);
+        if (num < 2) {
+            return false;
+        }
+        if (num % 2 == 0) {
+            return num == 2;
+        }
+        for (int divisor = 3; (long) divisor * divisor <= num; divisor += 2) {
+            if (num % divisor == 0) {
+                return false;
+            }
+        }
+        return true;
     }
 
 
diff --git a/src/test/java/algorithms/sprint4/MapTest.java b/src/test/java/algorithms/sprint4/MapTest.java
index 17de432..de9818b 100644
--- a/src/test/java/algorithms/sprint4/MapTest.java
+++ b/src/test/java/algorithms/sprint4/MapTest.java
@@ -1,11 +1,17 @@
 package algorithms.sprint4;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
 import java.util.OptionalInt;
 import org.junit.jupiter.api.Tag;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Timeout;
 
 @Tag("unit")
 class MapTest {
@@ -23,6 +29,23 @@ void hashTableSupportsPutGetUpdateAndDelete() {
         assertTrue(table.delete(1).isEmpty());
     }
 
+    @Test
+    @Timeout(10)
+    void readerReportsEndOfInputInsteadOfReplayingTheBuffer() throws IOException {
+        InputStream original = System.in;
+        try {
+            System.setIn(new ByteArrayInputStream("g 7".getBytes(StandardCharsets.UTF_8)));
+            Map.Reader reader = new Map.Reader();
+
+            assertEquals('g', reader.nextCommand());
+            assertEquals(7, reader.nextInt());
+            assertThrows(IOException.class, reader::nextCommand);
+            assertThrows(IOException.class, reader::nextInt);
+        } finally {
+            System.setIn(original);
+        }
+    }
+
     @Test
     void hashTableHandlesCollisionsAndNegativeKeys() {
         Map.HashTable table = new Map.HashTable();
diff --git a/src/test/java/kyu4/MorseCodeDecoderTest.java b/src/test/java/kyu4/MorseCodeDecoderTest.java
index 7bb562f..f2de84e 100644
--- a/src/test/java/kyu4/MorseCodeDecoderTest.java
+++ b/src/test/java/kyu4/MorseCodeDecoderTest.java
@@ -51,6 +51,7 @@ static Stream<Arguments> morseMessages() {
                 Arguments.of(".... . -.--", "HEY"),
                 Arguments.of("...---...", "SOS"),
                 Arguments.of("  .... . -.--   .--- ..- -.. .  ", "HEY JUDE"),
+                Arguments.of("---... -.-.-.", ":;"),
                 Arguments.of("", "")
         );
     }
diff --git a/src/test/java/kyu6/PrimeTest.java b/src/test/java/kyu6/PrimeTest.java
index 8d74901..09879d5 100644
--- a/src/test/java/kyu6/PrimeTest.java
+++ b/src/test/java/kyu6/PrimeTest.java
@@ -21,4 +21,16 @@ public class PrimeTest {
     void smokeTestsShouldExecuteApi() {
         quality.SmokeMethodTestHarness.verify(kyu6.Prime.class);
     }
+
+    @ParameterizedTest
+    @ValueSource(ints = {2, 3, 5, 7, 11, 13, 101, 7919, 2147483647})
+    void shouldAcceptPrimes(int candidate) {
+        assertTrue(isPrime(candidate));
+    }
+
+    @ParameterizedTest
+    @ValueSource(ints = {-7, -1, 0, 1, 4, 9, 15, 25, 49, 121, 7917, 2147483645})
+    void shouldRejectNonPrimes(int candidate) {
+        assertFalse(isPrime(candidate));
+    }
 }