#include "stdafx.h"
#include "math.h"
#include "iostream"
#include "iomanip"
using namespace std;


int main()
{
    int k , i , g = 1 , n = 0 ;
    cout << " Vvedite k = " ;
    cin >> k ;
    for (int i = 1; i <= k ; i ++)
    {
        g *= 3;
        n += g;
    }
    cout << " Summa pervih n chlenov ravna " << n << endl;


    return 0;
}