#include <bits/stdc++.h>
using namespace std;
#define int long long

signed main(){
  int n; cin >> n;
  int dp[n+1]; dp[0]=1; dp[1] = 1;
  for(int i=2; n>=i; ++i){
    dp[i] = dp[i-1]+dp[i-2];
  }
  cout << dp[n] << endl;
}