def digit_sum(a):
    a = str(a)
    cnt = 0
    for i in a:
        cnt += int(i)
    return cnt


def main():
    n = int(input())
    ans = n
    for i in range(n-1):
        ans = digit_sum(ans)
        if ans < 10:
            break
    print(ans)


if __name__ == "__main__":
    main()