#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
#define INF 1e9+7
#define n_max 1e9
typedef unsigned long long ll;
ll sum(ll l, ll r){
    ll sum = 0;
    for(ll i = l; i <= r; i+=2)
        sum += i;
    return sum;
}
int main()
{
    cin.tie();cout.tie(); ios_base::sync_with_stdio();
    ll l, r, k = 2;
    l = r = 1;
    int n;
    cin >> n;
    for(int i = 0; i < n-1; i++){
        l = r+2;
        r += k*2;
        k++;
    }
    //cout << l << ' ' << r << "\n";
    cout << sum(l,r);


    return 0;
}