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

public class Solution {

    

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int k = in.nextInt();
      

    
 int m=0,j=0,s=0,i;
        int a[]=new int[10000000];
    
    int l=(k*(k-1))/2;
    for(i=0;i<10000000;i++)
    {
        if(i%2!=0)
        {
            a[j++]=i;
        }
    }
    m=k;
    while(m>0)
    {
        s=s+a[l];
        l++;
        m--;
    }
    System.out.println(s);
    

    }
}