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

public class Solution {

    static long sumOfGroup(int k) {
        // Return the sum of the elements of the k'th group.
        int counter=1,num=0;
        long sum=0;
        for(int i=0;i<Math.pow(10,6);i++){
            if(i%2==0)
                continue;
            if(counter==k)
                sum+=i;
            num++;
            if(counter==k&&counter==num)
                break;
            if(num==counter){
                counter++;
                num=0;
                continue;
            }
        }
        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();
    }
    
  
}