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


signed main(){
    ios::sync_with_stdio(false);
	cin.tie(0);

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