p, q, r, k = map(int,input().split())

a = [-1] * 10000

a[0] = p % 10
a[1] = q % 10
a[2] = r % 10

for i in range(3, 100):
    x = (a[i - 1] + a[i - 2] + a[i - 3]) % 10
    if x in a[4:]:
        start = a.index(x)
        end = i
        a[i] = x
        break
    
    a[i] = x
if k < end:
    print(a[k - 1])
    exit()
ind = (k - 1 - start) % (end - start) + start

print(a[ind])