#define _CRT_SECURE_NO_DEPRECATE
#include<iostream>
#include<string>
#define MAX 51
using namespace std;
__int64 a[MAX];
__int64 _solv(__int64 i)
{
    if (a[i]){
        return a[i];
    }
    else{
        return a[i] = _solv(i - 1) + _solv(i - 2) * 2;
    }
}
int main()
{
    int n;
    memset(a, 0, sizeof(a));
    a[1] = 3; a[2] = 6; a[3] = 6;
    while (cin >> n){
        cout << _solv(n) << endl;
    }
    return 0;
}