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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.util.Scanner;


public class Star {
	public static void main(String[] args) {
		new Star().solve();
	}
	public void solve(){	
		Scanner in = new Scanner(System.in);
	    int input = in.nextInt();
	    int ans = recurse(input);
	    System.out.println(ans);

	}
	public int recurse(int input){
		if(input == 1){
			return 1;
		}
		int ans =(input -1)*12;
		return recurse(input-1)+ans;
	}

}
