#include <bits/stdc++.h>
using namespace std;
int main(){
  int n;
  cin >> n;
  vector<long long> fib(n + 1, 1);
  for (int i = 2; i <= n; i++){
    fib[i] = fib[i - 1] + fib[i - 2];
  }
  cout << fib[n] << endl;
}
