def sum_of_digits(n):
    """Sum digits of a number recursively."""
    if n == 0:
        return 0
    return n % 10 + sum_of_digits(n // 10)

print(sum_of_digits(1234))

def recursive_sum_of_digits(n):
    """
    Calculates the sum of digits of a non-negative integer using recursion.

    Args:
        n: The non-negative integer.

    Returns:
        The sum of its digits.
    """
    # Base case: if the number is 0, the sum of its digits is 0.
    if n == 0:
        return 0
    # Recursive case: add the last digit to the sum of digits of the remaining number.
    else:
        return (n % 10) + recursive_sum_of_digits(n // 10)

# Example Usage:
number = int(input("Enter a number  : "))
sum_digits = recursive_sum_of_digits(number)
print(f"The sum of digits of {number} is: {sum_digits}")

number_two = 789
sum_digits_two = recursive_sum_of_digits(number_two)
print(f"The sum of digits of {number_two} is: {sum_digits_two}")