#include<bits/stdc++.h>
using namespace std;
int main()
{
    long long a,b,c;
    c=1,a=1,b=1;
    int n;
    cin>>n;
    for(int i =3;i<=n+1;i++)
    {
        c=a+b;
        a=b;
        b=c;
    }
    cout<<c;
    return 0;
}
//😅😅😅😅😅😅😅😅😅