#include <stdio.h>
int main(void){
	long long f1,f2,val;
	scanf("%lld%lld%lld",&f1,&f2,&val);
	
	long long arr[val];
	arr[0] = f1;
	arr[1] = f2;
	for(int i = 2;i < val;i ++){
		arr[i] = arr[i - 1] ^ arr[i - 2];
	}
	printf("%lld",arr[val - 1]);
}