import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static long sumOfGroup(long k) {
          long n = ((k-1)*k) -1;
    long sum = 0;
    for(int i=1;i<=k;++i){
        n +=2;
        sum += n;
    }
    return sum;
    
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int k = in.nextInt();
        long answer = sumOfGroup(k);
        System.out.println(answer);
        in.close();
    }
}