// nemes tihamer 2020 masodik.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
#include <vector>


using namespace std;


void i_es_l_jardak() {
    int hossz; cin >> hossz;
    vector<long long>dpSi(hossz), dpSl(hossz);

    if (hossz < 2) {
        cout << 1;
        return;
    }
    dpSi[0] = 1;
    dpSi[1] = 2;
    dpSl[1] = 2;


    for (int i = 2; i < hossz; i++) {
        dpSl[i] = dpSl[i - 1] + dpSi[i - 2] * 2;
        dpSi[i] = dpSi[i - 1] + dpSi[i - 2] + dpSl[i - 1];
    }
    cout << dpSi[hossz - 1];

}


int main()
{
    cin.sync_with_stdio(false);
    cin.tie(nullptr);
    i_es_l_jardak();
}