p, q, r, K = map(int, input().split())
n = set()
o = []
p %= 10; q %= 10; r %= 10
n.add((p, q, r))
o.append([p, q, r])
for i in range(K-3):
    p, q, r = q, r, (p+q+r)%10
    if (p, q, r) in n:
        idx = o.index([p, q, r])
        p = (K-3-idx)%(len(o)-idx)
        pp, qq, rr = o[idx+p]
        print(rr)
        exit()
    else:
        n.add((p, q, r))
        o.append([p, q, r])
print(r)