def calculator():
    while True:
        print("\nOperations:")
        print("1. Addition")
        print("2. Subtraction")
        print("3. Multiplication")
        print("4. Division")
        print("5. Exit")

        choice = input("Enter operation number (1-5): ")

        if choice == '5':
            print("Exiting calculator.")
            break

        if choice not in ('1', '2', '3', '4'):
            print("Invalid input! Please enter a number between 1 and 5.")
            continue

        num1 = float(input("Enter first number: "))
        num2 = float(input("Enter second number: "))

        if choice == '1':
            print("Result:", num1 + num2)
        elif choice == '2':
            print("Result:", num1 - num2)
        elif choice == '3':
            print("Result:", num1 * num2)
        elif choice == '4':
            if num2 == 0:
                print("Error! Division by zero.")
            else:
                print("Result:", num1 / num2)

if __name__ == "__main__":
    calculator()