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

p %= 10
q %= 10
r %= 10
data = set((p, q, r))
array = [p, q, r]
while True:
    array.append((sum(array[-3:])%10))
    if tuple(array[-3:]) in data:
        break
    data.add(tuple(array[-3:]))
for i in range(len(array)-3):
    if array[i:i+3] == array[-3:]:
        start = i
        break
cycle = len(array) - 3 - start


target_index = (K-start) % cycle
result = array[target_index]
print(result)