Problem Description

Given an $n \times n$ square board, several players are playing tic-tac-toe on it.

The rules of tic-tac-toe are: each player takes turns writing a letter, and all letters written by the same player are identical. If a player forms $3$ consecutive copies of their own letter in a row, a column, or a diagonal, then that player wins.

Given the current state of the board, find the winning player.

Input Format

The first line contains an integer $n$.

The next $n$ lines each contain $n$ characters, which are either uppercase letters or . (meaning no one has played on that cell).

Output Format

Output one uppercase letter on a single line, representing the letter written by the winning player.

If no one has won, output ongoing.

The testdata guarantees that at most one player has won.

3
XOC
XOC
X..

X

4
....
..A.
AAB.
.B.B

ongoing

3
ABB
AAA
BBA

A

Hint

Constraints

For $100\%$ of the testdata, $1 \le n \le 30$.

Notes

This problem is translated from COCI2006-2007 CONTEST #6 T3 MARATON。

Translated by ChatGPT 5