#!/usr/bin/env python3
#fileencoding: utf-8

f0, f1, N = [int(i) for i in input().strip().split(" ")]

if N <= 2:
    print([f0,f1,f0^f1][N])
else:
    fk_1 = f0 + f1
    fk_2 = f1
    f = 0
    for i in range(N-2):
        fk_1, fk_2 = fk_1^fk_2, fk_1
        f = fk_1
    print(f)