# No.64 XORフィボナッチ数列
f0, f1, n = [int(i) for i in input().split()]
f = 0

if n == 0:
    print(f0)
elif n == 1:
    print(f1)
else:
    for i in range(n - 1):
        f = f0 ^ f1
        f0 = f1
        f1 = f
    print(f)