#include <iostream>
#include <fstream>

using namespace std;

long long fibo(int n){
    if(n==1){
        return 1;
    }
    else if(n==2){
        return 2;
    }
    else{
        long long a = 1, b = 2, c;
        for(int i = 3; i <= n; i++){
            c = a + b; 
            a = b;
            b = c;
        }
        return c;
    }
}

ifstream f("nunta.in");
ofstream g("nunta.out");

int main(){
    int n; 
    f>>n;
    long long nr = fibo(n);
    g<<nr;
    cout<<nr;
}