#coding: utf-8
##yuki_64

s=map(int,raw_input().split())

f0=s[0]
f1=s[1]
n=s[2]

def xfib(m):
 if m==0:
  return f0
 elif m==1:
  return 1
 else:
  x,y = f0,f1
  while m > 1:
   m,x,y=m-1,y,x^y
 return y

print(xfib(n))