from collections import defaultdict
p, q, r, k = map(int, input().split())
s = (int(str(p)[-1]), int(str(q)[-1]), int(str(r)[-1]))
s_dic = defaultdict(int)
s_dic[s] = 1
loop_list = [s]
flg = 0
for i in range(k - 3):
    s = (s[1], s[2], int(str(sum(s))[-1]))
    if s_dic[s]:
        flg = 1
        break
    else:
        s_dic[s] = 1
        loop_list.append(s)
if flg:
    k -= 2
    k %= len(loop_list)
    print(loop_list[k - 1][-1])
else:
    print(s[-1])