题解 | #等差数列#

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.text.DateFormat;
import java.text.DecimalFormat;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;
import java.util.*;
import java.util.stream.IntStream;
import java.util.stream.Stream;

import static java.util.Arrays.*;
import static java.util.stream.Stream.*;

public class Main {
    public static void main(String[] args) throws IOException {

        testTh();
    }

    private static void testTh() throws IOException {
        BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
        String str;
        while ((str = bf.readLine()) != null) {
            int parseInt = Integer.parseInt(str);
            System.out.println((3 * parseInt + 1) * parseInt / 2);


        }

    }




}