while True:
    try:
        num1 = float(input("Enter the first number: "))
        num2 = float(input("Enter the second number: "))
        
        print("Select an operation:")
        print("1. Addition")
        print("2. Subtraction")
        print("3. Multiplication")
        print("4. Division")
        
        operation = int(input("Enter the operation number (1/2/3/4): "))
        
        if operation == 1:
            result = num1 + num2
        elif operation == 2:
            result = num1 - num2
        elif operation == 3:
            result = num1 * num2
        elif operation == 4:
            if num2 != 0:
                result = num1 / num2
            else:
                print("Error: Division by zero")
                continue
        else:
            print("Invalid operation")
            continue
        
        print("Result:", result)
        
        user_input = input("Do you want to perform another calculation? (yes/no): ")
        if user_input.lower() != "yes":
            break
    except ValueError:
        print("Invalid input. Please enter valid numbers.")