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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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class P171B_Star {

    public static void main(String[] args) throws IOException {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        int a = Integer.parseInt(in.readLine());
        System.out.println(1+12*sum(a-1));
    }
    
    public static int sum(int n) {
        return (n+1)*n/2;
    }

}
