#include<bits/stdc++.h>
using namespace std;
signed main()
{
    ios::sync_with_stdio(false);
    int n,ans=1,ans1=1,ans2;cin>>n;
    for(int i=1;i<=n+1;i++) {ans2=ans+ans1;swap(ans,ans1);swap(ans1,ans2);}
    cout<<ans2;
    return 0;
}