#include <bits/stdc++.h>
using namespace std;
const double PI = acos(-1.0);
long long f[22];
int main() {
  int a, b, c;
  while (cin >> a >> b >> c) {
    f[0] = a;
    f[1] = b;
    for (int i = (2), _b = (c); i <= _b; i++) f[i] = f[i - 1] + f[i - 2];
    cout << f[c] << endl;
  }
  return 0;
}
