p, q, r, k = map(int, input().split())
p %= 10
q %= 10
r %= 10
a = [p, q, r]

idx = {}
period = 0
for i in range(k - 3):
    x = 100*a[-3] + 10*a[-2] + a[-1]
    if x not in idx:
        idx[x] = i + 3
    else:
        period = i + 3 - idx[x]
        idx[x] = i + 3
        break
    a.append(sum(a[-3:]) % 10)
    if i == k - 4:
        print(a[-1])
        exit()

last = 0
for x, v in idx.items():
    if (k - 1 - v) % period == 0 and v > last:
        ans = (x // 100 + x // 10 + x) % 10
        last = v
print(ans)