// UUID: fc96909c-f712-408e-baf4-54b4cb9d76a2
#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
	ios::sync_with_stdio(false);
    cin.tie(0);
    
    int n; cin >>n;

    array<int,28>eg, feu, leu;

    eg[0] = 1;
    eg[1] = 2;

    feu[0] = 1;
    feu[1] = 1;

    leu[0] = 1;
    leu[1] = 1;

    for (int i = 2; i < n; i++){
        eg[i] = eg[i-2]+eg[i-1]+feu[i-1]+leu[i-1];
        feu[i] = eg[i-2]+leu[i-1];
        leu[i] = eg[i-2]+feu[i-1];

    }

    cout << eg[n-1];
}