котик

int main() {
    int a,b,c,i,d;
    cin>>a;
    b = 1;
    c = 1;
    if (a == 1){
        cout<<2;
    }
    else{
        for(i=0;i<a-1;++i){
            d = c;
            c = c + b;
            b = d;
        }

    }
    cout<<b+c;



    cout<<"\n";
    return 0;
}