Timus_1225

//Timus 1225
#include <iostream>
using namespace std;
void recurse(long long int n, long long int as, long long int bs, long long int sums, long long int pras, long long int ys)
{
    if(ys!=n)
    {
        sums=bs+as;
        pras=as;
        as=bs;
        bs=pras+bs;
        ys++;
        recurse(n, as, bs, sums, pras, ys);
    }
    else
    {
       cout<<sums<<endl;
    }
}
int main()
{
    long long int s, a=0, b=2, sum=1, pra=1, y=1;
    cin>>s;
    if(s==1){cout<<"2"<<endl;}
    else if(s==2){cout<<"2"<<endl;}
    else{recurse(s,a,b,sum,pra,y);}
    return 0;
}