#include <bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimization("O3")
#pragma GCC optimization("unroll-loops")
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int a[100], in, sum = 0;
  cin >> a[0] >> a[1] >> in;
  sum = a[0] + a[1];
  a[2] = sum;
  for (int i = 2; i < in + 1; i++) a[i] = a[i - 1] + a[i - 2];
  cout << a[in];
  return 0;
}
