#include <iostream>

using namespace std;

int main() {

    setlocale(LC_ALL, "ru");

    int count;
    cout << "Введите число: ";
    cin >> count;

    int result = 0;

    for (int i = 0; i < count; i++) {
        result += 15 + i * 2;
    }

    cout << result << endl;


}