#include <bits/stdc++.h>
using namespace std;
long long x, y, n;
long long arr[6];
int main() {
  ios_base::sync_with_stdio(0);
  cin >> x >> y >> n;
  int pos = (n - 1) % 6;
  arr[0] = (x + 1000000007) % 1000000007;
  arr[1] = (y + 1000000007) % 1000000007;
  arr[2] = (y - x + 1000000007 + 1000000007) % 1000000007;
  arr[3] = (-x + 1000000007) % 1000000007;
  arr[4] = (-y + 1000000007) % 1000000007;
  arr[5] = (x - y + 1000000007 + 1000000007) % 1000000007;
  cout << arr[pos] << endl;
  return 0;
}
