mod = 1000000007
eps = 10**-9


def main():
    import sys
    input = sys.stdin.readline

    N = input().rstrip('\n')
    for _ in range(100):
        NN = 0
        for n in N:
            NN += int(n)
        N = str(NN)
    print(NN)


if __name__ == '__main__':
    main()