#include <bits/stdc++.h>
int t[23] = {};
int main() {
  int a, b, c;
  scanf("%d%d%d", &a, &b, &c);
  t[0] = a;
  t[1] = b;
  for (int i = 2; i <= c; i++) t[i] = t[i - 2] + t[i - 1];
  printf("%d\n", t[c]);
  scanf(" ");
}
