#include <iostream>
using namespace std;

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