读入一个整数，表示井字棋棋盘的边长。判断其中是否存在某一方获胜，获胜的条件是存在整行或整列或整条对角线或整条反对角线上是相同的棋子。如果存在，则输出代表获胜一方字母：X或O（大写字母X或O）；如果没有任何一方获胜，则输出NIL。-Read an integer, said tic-tac-toe chess board side length. Determine whether there is a party wins, the winning condition is the entire line or the entire column or diagonal or whole on the diagonal is the same. If present, indicates that the output on behalf of the winning side letter: X or O (uppercase X or O)　If no one wins, then the output is NIL.