def is_armstrong(num):
    temp = num
    sum_of_cubes = 0
    while temp > 0:
        digit = temp % 10
        sum_of_cubes += digit ** 3
        temp //= 10
    if sum_of_cubes == num:
        print(num, "is an Armstrong number.")
    else:
        print(num, "is not an Armstrong number.")

is_armstrong(153)

153 is an Armstrong number.

is_armstrong(123)

123 is not an Armstrong number.