#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, b, c;
  scanf("%d%d%d", &a, &b, &c);
  if (c == 1) {
    printf("%d", b);
    return 0;
  }
  for (int i = 2; i <= c; i++) {
    int d = a + b;
    a = b;
    b = d;
  }
  printf("%d", b);
  return 0;
}
