class TicTacToeBoard:
    def __init__(self, size):
        self.size = size
        
        # construct a new board that is size by size
        self.board = []
        
        for i in range(self.size):
            self.board.append(["_"] * size)
            
    def add_X(self, row, col):
        self.add_mark("X", row, col)
        
    def add_O(self, row, col):
        self.add_mark("O", row, col)
        
    def add_mark(self, mark, row, col):
        if self.board[row][col] != "_":
            return False
        else:
            self.board[row][col] = mark
            
    def is_game_over(self):
        return self.is_full() or self.has_win()
        
    def is_full(self):
        for r in range(self.size):
            for c in range(self.size):
                if self.board[r][c] == "_":
                    return False
                
        return True
            
    def has_win(self):
        # check the rows
        for r in range(self.size):
            if self.is_row_all_mark("X", r) or \
               self.is_row_all_mark("O", r):
                return True
            
        # check the columns
        for c in range(self.size):
            if self.is_col_all_mark("X", c) or \
               self.is_row_all_mark("O", c):
                return True
            
        # check the diagonals
        if self.is_diagonal_all_mark("X") or \
           self.is_diagonal_all_mark("O") or \
           self.is_other_diagonal_all_mark("X") or \
           self.is_other_diagonal_all_mark("O"):
            return True
        
        return False
        
        
    def is_row_all_mark(self, mark, row):
        for c in range(self.size):
            if self.board[row][c] != mark:
                return False
            
        return True
    
    def is_col_all_mark(self, mark, col):
        for r in range(self.size):
            if self.board[r][col] != mark:
                return False
            
        return True
    
    def is_diagonal_all_mark(self, mark):
        for i in range(self.size):
            if self.board[i][i] != mark:
                return False
            
        return True
    
    def is_other_diagonal_all_mark(self, mark):
        for i in range(self.size):
            if self.board[i][self.size - 1 - i] != mark:
                return False
            
        return True
        
    def __str__(self):
        board_string = "    "
        
        # add the column indices at the top
        for i in range(self.size):
            board_string += str(i) + "    "
            
        board_string += "\n"
        
        for i in range(self.size):          
            board_string += str(i) + " " + str(self.board[i]) + "\n"
            
        return board_string
                
def play_game():
    board = TicTacToeBoard(3)
    
    x_turn = True
    
    while not board.is_game_over():
        print board
        print
        
        if x_turn:
            print "X's turn"
            mark = "X"
        else:
            print "O's turn"
            mark = "O"
            
        selection = raw_input("Enter-row col: ").split()
        row = int(selection[0])
        col = int(selection[1])
        
        board.add_mark(mark, row, col)
        
        # change the turn
        x_turn = not x_turn
        
    print board
    print 
    
    if board.has_win():
        if x_turn:
            print "O wins!"
        else:
            print "X wins!"
    else:
        print "It's a tie!"
        
play_game()