#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 20 + 10;
int ans[MAX_N];
int main() {
  int a[3];
  for (int i = 0; i < 3; i++) {
    cin >> a[i];
  }
  ans[0] = a[0];
  ans[1] = a[1];
  for (int i = 2; i <= a[2]; i++) {
    ans[i] = ans[i - 1] + ans[i - 2];
  }
  cout << ans[a[2]];
}
