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

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