#include <bits/stdc++.h>
using namespace std;
const int maxint = -1u >> 1;
template <class T>
bool get_max(T& a, const T& b) {
  return b > a ? a = b, 1 : 0;
}
template <class T>
bool get_min(T& a, const T& b) {
  return b < a ? a = b, 1 : 0;
}
int main() {
  int f[21];
  int a, b, c;
  cin >> a >> b >> c;
  f[0] = a;
  f[1] = b;
  for (int i = 2; i < 21; i++) f[i] = f[i - 1] + f[i - 2];
  cout << f[c] << endl;
  return 0;
}
