diff --git a/src/main/java/school/lemon/changerequest/java/introduction/pr1/ConsoleCalculator.java b/src/main/java/school/lemon/changerequest/java/introduction/pr1/ConsoleCalculator.java
index da96e86..062965b 100644
--- a/src/main/java/school/lemon/changerequest/java/introduction/pr1/ConsoleCalculator.java
+++ b/src/main/java/school/lemon/changerequest/java/introduction/pr1/ConsoleCalculator.java
@@ -1,9 +1,98 @@
 package school.lemon.changerequest.java.introduction.pr1;
 
 
+import java.util.Scanner;
+
 public class ConsoleCalculator {
 
     public static void main(String[] args) {
+        System.out.println("Console calculator:");
+        System.out.println("Enter 'add' to perform addition.");
+        System.out.println("Enter 'sub' to perform subtraction.");
+        System.out.println("Enter 'mul' to perform multiplication.");
+        System.out.println("Enter 'div' to perform division.");
+        System.out.println("Enter 'exit' to exit.");
+        System.out.println("Enter 'help' to see help message.");
+        boolean start = true;
+        while (start) {
+            System.out.println("Make your choice.");
+            Scanner sc = new Scanner(System.in);
+            String choice = sc.nextLine();
+            choice.toLowerCase();
+            switch (choice) {
+                case "add":
+                    add();
+                    break;
+                case "sub":
+                    sub();
+                    break;
+                case "mul":
+                    mul();
+                    break;
+                case "div":
+                    div();
+                    break;
+                case "exit":
+                    exit();
+                    break;
+                case "help":
+                    help();
+                    break;
+                default:
+            }
+        }
+
+
+    }
+
+    private static void help() {
+    }
+
+    private static void exit() {
+        System.out.println("Bye-bye");
+        System.exit(0);
+    }
+
+    private static void div() {
+        Scanner sc = new Scanner(System.in);
+        int a, b, result;
+        System.out.println("Enter first number:");
+        a = sc.nextInt();
+        System.out.println("Enter second number:");
+        b = sc.nextInt();
+        result = a / b;
+        System.out.println("Result of " + a + "/" + b + " is " + result);
+    }
+
+    private static void mul() {
+        Scanner sc = new Scanner(System.in);
+        int a, b, result;
+        System.out.println("Enter first number:");
+        a = sc.nextInt();
+        System.out.println("Enter second number:");
+        b = sc.nextInt();
+        result = a * b;
+        System.out.println("Result of " + a + "*" + b + " is " + result);
+    }
+
+    private static void sub() {
+        Scanner sc = new Scanner(System.in);
+        int a, b, result;
+        System.out.println("Enter first number:");
+        a = sc.nextInt();
+        System.out.println("Enter second number:");
+        b = sc.nextInt();
+        result = a - b;
+        System.out.println("Result of " + a + "-" + b + " is " + result);
+    }
 
+    private static void add() {
+        Scanner sc = new Scanner(System.in);
+        int a, b;
+        System.out.println("Enter first number:");
+        a = sc.nextInt();
+        System.out.println("Enter second number:");
+        b = sc.nextInt();
+        System.out.println("Result of " + a + "+" + b + " is " + a + b);
     }
 }
diff --git a/src/main/java/school/lemon/changerequest/java/introduction/pr1/HammingDistance.java b/src/main/java/school/lemon/changerequest/java/introduction/pr1/HammingDistance.java
index b8a218f..bf63771 100644
--- a/src/main/java/school/lemon/changerequest/java/introduction/pr1/HammingDistance.java
+++ b/src/main/java/school/lemon/changerequest/java/introduction/pr1/HammingDistance.java
@@ -2,6 +2,19 @@
 
 public class HammingDistance {
     public static int compute(String a, String a1) {
+        int la = a.length();
+        int la1 = a1.length();
+        int count = 0;
+
+        if (la == la1) {
+            for (int i = 0; i < la; i++) {
+                if (a.charAt(i) != a1.charAt(i))
+                    count++;
+            }
+            return count;
+        }
         return -1;
     }
+
+
 }