#!/usr/bin/env python3
from typing import *

def solve(n: int) -> int:
    for _ in range(99):
        n = sum(map(int, str(n)))
    return n

# generated by online-judge-template-generator v4.5.0 (https://github.com/kmyk/online-judge-template-generator)
def main():
    N = int(input())
    a = solve(N)
    print(a)

if __name__ == '__main__':
    main()