#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  long long int i, F0, F1, N;
  scanf("%ld %ld %ld", &F0, &F1, &N);
  long long int* array = (long int*)malloc(N * sizeof(long int));

  array[0] = F0;
  array[1] = F1;
  for (i = 2; i < N+1; i++)
    array[i] = array[i-1] ^ array[i-2];
  
  printf("%ld\n", array[N]);

  return 0;
}