F0, F1, N = map(int, input().split())
if N==0:
    print(F0)
    exit()
if N==1:
    print(F1)
    exit()
N %= 3
N -= 1
F = [F0, F1]
for i in range(N):
    F.append(F[-1]^F[-2])
print(F[-1])