diff --git a/buggyCalculator.ts b/buggyCalculator.ts
index a8bde8b..c233bd0 100644
--- a/buggyCalculator.ts
+++ b/buggyCalculator.ts
@@ -9,13 +9,7 @@ function subtract(a: number, b: number): number {
 }
 
 function multiply(a: number, b: number): number {
-    let result = 0;
-
-    for (let i = 0; i < a; i++) {
-        result += b;
-    }
-
-    return result;
+    return a * b;
 }
 
 function divide(a: number, b: number): number {
@@ -39,41 +33,65 @@ console.log("4. Divide");
 
 rl.question("Choice: ", (choice) => {
 
+    if (!["1", "2", "3", "4"].includes(choice)) {
+        console.error("Unknown operation. Please enter a number between 1 and 4.");
+        rl.close();
+        return;
+    }
+
     rl.question("First number: ", (n1) => {
 
-        rl.question("Second number: ", (n2) => {
+        const num1 = parseInt(n1);
 
-            const num1: number = parseInt(n1);
-            const num2: number = parseInt(n2);
+        if (isNaN(num1)) {
+            console.error("Invalid input. Please enter a valid number.");
+            rl.close();
+            return;
+        }
 
-            let result: number;
+        rl.question("Second number: ", (n2) => {
 
-            if (choice === "1") {
-                result = add(num1, num2);
-            } else if (choice === "2") {
-                result = subtract(num1, num2);
-            } else if (choice === "3") {
-                result = multiply(num1, num2);
-            } else if (choice === "4") {
-                result = divide(num1, num2);
-            } else {
-                console.log("Unknown operation");
+            const num2 = parseInt(n2);
+
+            if (isNaN(num2)) {
+                console.error("Invalid input. Please enter a valid number.");
+                rl.close();
                 return;
             }
 
-            console.log("Result:", result);
+            let result: number;
+
+            try {
+                switch (choice) {
+                    case "1":
+                        result = add(num1, num2);
+                        break;
+                    case "2":
+                        result = subtract(num1, num2);
+                        break;
+                    case "3":
+                        result = multiply(num1, num2);
+                        break;
+                    case "4":
+                        result = divide(num1, num2);
+                        break;
+                    default:
+                        throw new Error("Unknown operation");
+                }
+
+                console.log("Result:", result);
+            } catch (error) {
+                if (error instanceof Error) {
+                    console.error(`Error: ${error.message}`);
+                } else {
+                    console.error("An unknown error occurred");
+                }
+            } finally {
+                rl.close();
+            }
 
-            rl.close();
         });
 
     });
 
-});
-
-function factorial(n: number): number {
-    if (n === 0 || n === 1) {
-        return 1;
-    }
-
-    return n * factorial(n - 1);
-}
\ No newline at end of file
+});
\ No newline at end of file