#include <fstream>
#include <vector>

using namespace std;

ifstream fin("nunta.in");
ofstream fout("nunta.out");

const int base= 10;

void h_write( vector <int> x ) {
    for ( int i= (int)x.size()-1; i>=0; --i ) {
        fout<<x[i];
    }
    fout<<"\n";
}

void hh_add( vector <int> &x, vector <int> y ) {
    int t= 0;
    for ( int i= 0; i<(int)x.size() || i<(int)y.size() || t>0; ++i ) {
        if ( i>=(int)x.size() ) {
            x.push_back(0);
        }
        x[i]+= y[i]+t;
        t= x[i]/base;
        x[i]%= base;
    }
}

int main(  ) {
    int n;
    fin>>n;
    if ( n<=3 ) {
        fout<<n<<"\n";
        return 0;
    }
    n-= 3;

    vector <int> f1, f2;
    f1.push_back(3);
    f2.push_back(2);
    while ( n>0 ) {
        vector <int> aux= f1;
        hh_add(f1,f2);
        f2= aux;
        --n;
    }

    h_write(f1);

    return 0;
}