#include <bits/stdc++.h>
using namespace std;
const int maxA = 20 + 10;
int a1, a2, a3, f[maxA], ans;
int main() {
  cin >> a1 >> a2 >> a3;
  f[0] = a1;
  f[1] = a2;
  for (int i = 2; i <= a3; i++) {
    f[i] = f[i - 1] + f[i - 2];
  }
  cout << f[a3];
  return 0;
}
