# import sys; input = sys.stdin.buffer.readline
# sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	N = input()
	for i in range(100):
		N = sum(list(map(int, list(N))))
		N = str(N)

	print(N)




if __name__ == '__main__':
	main()