import sys


def input(): return sys.stdin.readline().rstrip('\n')


def main():
    p, q, r, k = map(int, input().split())
    st = (p % 10, q % 10, r % 10)
    a = {st: 3}
    for i in range(4, k + 1):
        p, q, r = st
        p, q, r = q, r, (p + q + r) % 10
        if (p, q, r) in a:
            md = i - a[(p, q, r)]
            to_go = (k - i) % md
            for _ in range(to_go):
                p, q, r = q, r, (p + q + r) % 10
            break
        st = (p, q, r)

    return r


if __name__ == '__main__':
    ret = main()
    if ret is not None:
        print(ret)