p,q,r,k = map(int,input().split())
k -= 4
p %= 10
q %= 10
r %= 10
l = [[p,q,r]]
vis = []
for i in range(10):
    vis.append([[0] * 10 for _ in range(10)])
vis[p][q][r] = 1
cnt = 1
start = 0
leg = 10 ** 3 + 1
for i in range(min(10 ** 3 + 1,k)):
    o_l = l[i][1::]
    l.append(o_l + [sum(l[i])% 10])
    x,y,z = l[i+1]
    if vis[x][y][z] != 0:
        leg = cnt + 1 - vis[x][y][z]
        start = vis[x][y][z]
        break
    cnt += 1
    vis[x][y][z] = cnt
    
k = k - start
amari = k % leg
print(sum(l[start + amari]) % 10)