#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ul;
typedef signed long long ll;
ul over = 1000000007;

int main(void)
{
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed;
  int n;
  cin >> n;
  ll dp[n+1];
  dp[0] = 1;
  dp[1] = 1;
  for (int i = 2; i <= n; ++i) {
    dp[i] = dp[i-1] + dp[i-2];
  }
  cout << dp[n] << endl;
  return 0;
}