import collections
from itertools import count

p, q, r, K = map(int, input().split())

p %= 10
q %= 10
r %= 10
memo = collections.defaultdict(int)
memo[p, q, r] = 2
a = [p, q, r]
for i in count(3):
    x = (a[-1] + a[-2] + a[-3]) % 10
    a.append(x)
    if i == K:
        print(a[-1])
        break

    key = (a[-3], a[-2], a[-1])
    if key in memo: # found cycle
        loop_start = memo[key]
        loop_len = i - loop_start
        index = ((K - 1) - loop_start) % loop_len + loop_start
        print(a[index])
        break
    memo[key] = i