P, Q, R, K = [int(x) for x in input().split()]
P %= 10; Q %= 10; R %= 10
p, q, r = P, Q, R
lst = [p, q, r]
for i in range(K-3):
    p,q,r = q,r,p+q+r
    p %= 10; q %= 10; r %= 10
    lst.append(r)
    if (p,q,r) == (P, Q, R):
        break
if len(lst) == K:
    print(lst[-1])
else:
    l = len(lst) - 3
    print(lst[(K-1)%l])