diff --git a/src/main/java/Challenges.java b/src/main/java/Challenges.java
index b5acedd..24d835f 100644
--- a/src/main/java/Challenges.java
+++ b/src/main/java/Challenges.java
@@ -64,8 +64,7 @@ public String[] circularArray(int index) {
         System.arraycopy(COUNTRY_NAMES, index, tempArray, 0, numberOfElementsToCopy);
         System.arraycopy(COUNTRY_NAMES, 0, tempArray, numberOfElementsToCopy, COUNTRY_NAMES.length - numberOfElementsToCopy);
 
-        COUNTRY_NAMES = tempArray.clone();
-        return COUNTRY_NAMES;
+        return tempArray.clone();
     }
 
     ;
@@ -91,17 +90,18 @@ public String[] circularArray(int index) {
     ***** */
 
     public String ownPower(int number, int lastDigits) {
-        BigInteger powResult = BigInteger.ZERO;
+        BigInteger moduloNumber = BigInteger.TEN.pow(lastDigits);
+        BigInteger moduloAddition = BigInteger.ZERO;
 
         for (int i = 1; i <= number; i++) {
-            BigInteger powNumber = new BigInteger(String.valueOf(i)).pow(i);
+            BigInteger resultModuloPow = BigInteger.valueOf(i).modPow(BigInteger.valueOf(i), moduloNumber);
 
-            powResult = powResult.add(powNumber);
+            moduloAddition = moduloAddition.add(resultModuloPow).mod(moduloNumber);
         }
 
-        String result = String.valueOf(powResult);
+        String result = String.valueOf(moduloAddition);
 
-        return result.substring(result.length() - lastDigits);
+        return "0".repeat(lastDigits - result.length()).concat(result);
     }
 
     ;
@@ -125,17 +125,15 @@ A factorial (x!) means x! * (x - 1)... * 3 * 2 * 1.
 
     public Integer digitSum(int n) {
         BigInteger totalFactorial = BigInteger.ONE;
+        BigInteger sum = BigInteger.ZERO;
 
         for (int i = n; i >= 1; i--) {
             totalFactorial = totalFactorial.multiply(BigInteger.valueOf(i));
         }
 
-        char[] digits = String.valueOf(totalFactorial).toCharArray();
-
-        BigDecimal sum = BigDecimal.ZERO;
-
-        for (char c : digits) {
-            sum = sum.add(new BigDecimal(String.valueOf(c)));
+        while (totalFactorial.compareTo(BigInteger.ZERO) > 0) {
+            sum = sum.add(totalFactorial.mod(BigInteger.TEN));
+            totalFactorial = totalFactorial.divide(BigInteger.TEN);
         }
 
         return sum.intValue();