"""
 sum.py
 
 Write a function sum_1_to_n(n) that adds the integers 1 to n.
 Ask the user for n ; call this function ; output the result
 
 in class exercise , March 22.

    $ python sum.py
    What is n? 10
    The sum of 1 to 10 is 55.

 Jim M
"""

def sum_1_to_n(n):
    """ return 1 + 2 + 3 + ... + n """
    result = 0
    for i in range(1, n+1):
        result = result + i
    return result

def main():
    number_string = input("What is n? ")
    number = int(number_string)
    answer = sum_1_to_n(number)
    print(f"The sum of 1 to {number} is {answer}.")

main()