p,q,r,K = map(int,input().split())
dp = [p%10,q%10,r%10]
while True:
    dp.append(sum(dp[-3:])%10)
    if dp[:3] == dp[-3:]:
        break
for _ in range(3): dp.pop()
L = len(dp)
print(dp[(K-1)%L])