import sys
input=sys.stdin.readline
def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))

def main():
    mod=10**9+7
    N=I()
    
    def calc(X):
        temp=0
        while X!=0:
            temp+=X%10
            X=X//10
        return temp
    
    ans=N
    for i in range(99):
        ans=calc(ans)
        
    print(ans)
    


main()