def add(x, y):
    return x + y

def subtract(x, y):
    return x - y

def multiply(x, y):
    return x * y

def divide(x, y):
    if y != 0:
        return x / y
    else:
        return "Cannot divide by zero"

while True:
    print("Select operation:")
    print("1. Addition")
    print("2. Subtraction")
    print("3. Multiplication")
    print("4. Division")
    print("5. Exit")

    choice = input("Enter choice (1/2/3/4/5): ")

    if choice == '5':
        print("Calculator exiting. Goodbye!")
        break

    if choice in ('1', '2', '3', '4'):
        num1 = float(input("Enter first number: "))
        num2 = float(input("Enter second number: "))

        if choice == '1':
            print("Add =" , num1 + num2)
        elif choice == '2':
            print("Subtract =" , num1 - num2)
        elif choice == '3':
            print("multiply =" , num1 * num2)
        elif choice == '4':
            print("divide =" , num1 / num2)
    else:
        print("Invalid input. Please enter a valid number (1/2/3/4/5).")