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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;
import java.util.StringTokenizer;

public class Solution
{
    BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = null;

    private void solve() throws IOException
    {
        int n = nextInt();
        long a[] = new long[n + 1];
        a[1] = 1;
        int kk = 2;
        for(int i = 2; i <= n; i++)
        {
            a[i] = a[i - 1] + 6 * kk;
            kk += 2;
        }
        
        System.out.println(a[n]);
    }
    
    String nextToken() throws IOException
    {
        if (st == null || !st.hasMoreTokens())
        {
            st = new StringTokenizer(bf.readLine());
        }
        
        return st.nextToken();
    }

    int nextInt() throws IOException
    {
        return Integer.parseInt(nextToken());
    }

    long nextLong() throws IOException
    {
        return Long.parseLong(nextToken());
    }

    double nextDouble() throws IOException
    {
        return Double.parseDouble(nextToken());
    }

    public static void main(String args[]) throws IOException
    {
        new Solution().solve();
    }
    
}