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Input

The input contains a single integer a (1 ≤ a ≤ 18257).

Output

Print a single integer output (1 ≤ output ≤ 2·109).

Examples

Input

2


Output

13
import java.io.*;
public class Main
{
 public static void main(String[] args) throws IOException
    { 
    
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int n= Integer.parseInt(br.readLine());

long c = 0;
int i = 0 ;
while(i<n)
{
    c = c+i*12;
    i++;
}
System.out.println(c+1);
}
}