import sys
def main():
    input = sys.stdin.readline
    P, Q, R, K = map(int, input().split())
    S = set()
    L = list()
    for i in range(1000):
        if (P, Q, R) in S:
            j = L.index((P, Q, R))
            break
        S.add((P, Q, R))
        L.append((P, Q, R))
        P, Q, R = Q, R, (P + Q + R) % 10
    K -= 4
    if K <= i:
        print(sum(L[K]) % 10)
        return
    K -= i
    c = i - j
    K %= c
    print(sum(L[j + K]) % 10)

if __name__ == '__main__':
    main()