p,q,r,K = map(int, input().split())
memo = [-1] * 2000
memo[1] = p % 10
memo[2] = q % 10
memo[3] = r % 10

cycle = -1
for i in range(1001):
    memo[4+i] = (memo[3+i] + memo[2+i] + memo[1+i]) % 10
    if memo[4+i] == memo[3] and memo[3+i] == memo[2] and memo[2+i] == memo[1]:
        cycle = i+1
        break

print(memo[(K-1)%cycle+1])