from collections import deque

p, q, r, K = map(int, input().split())
K -= 3
p, q, r = p % 10, q % 10, r % 10
que = deque()
vis = set()
for _ in range(1000):
    now = p * 100 + q * 10 + r
    if now in vis:
        break
    vis.add(now)
    que.append(now)
    p, q, r = q, r, (p + q + r) % 10
while que[0] != now and K:
    que.popleft()
    K -= 1
K %= len(que)
while K:
    que.popleft()
    K -= 1
print(que[0] % 10)