#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll F[51];

ll SFB(){
     F[1]=1;
     F[2]=1;
    for(ll i=3 ; i<=51 ;i++){
        F[i] = F[i-1] + F[i-2];
    }
}

int main(){
    SFB();
    int n; cin >>n;
    cout<<F[n+1];
return 0;
}