LineInverter

using System;
using System.Linq;

class LineInverter
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine());
        char[][] matrix = new char[n][];
        for (int i = 0; i < n; i++)
        {
            matrix[i] = Console.ReadLine().ToCharArray();
        }
        int minSteps = 0;

        while (true)
        {
            if (IsBlack(matrix) || minSteps > n * n)
            {
                break;
            }
            var bestRow = FindBestRow(matrix);
            var bestCol = FindBestCol(matrix);
            if (bestRow.Item2 >= bestCol.Item2)
            {
                InvertRow(bestRow.Item1, matrix);
            }
            else
            {
                InvertCol(bestCol.Item1, matrix);
            }
            minSteps++;
        }
        Console.WriteLine(minSteps > n * n ? -1 : minSteps);
    }

    private static bool IsBlack(char[][] matrix)
    {
        int blackCount = matrix.Sum(m => matrix.Where((t, col) => m[col] == 'B').Count());
        return blackCount == matrix.Length*matrix.Length;
    }

    private static Tuple<int, int> FindBestCol(char[][] matrix)
    {
        int bestCol = 0;
        int bestCount = 0;
        for (int col = 0; col < matrix.Length; col++)
        {
            int count = matrix.Count(t => t[col] == 'W');
            if (count > bestCount)
            {
                bestCount = count;
                bestCol = col;
            }
        }
        return new Tuple<int, int>(bestCol, bestCount);
    }

    private static Tuple<int, int> FindBestRow(char[][] matrix)
    {
        int bestRow = 0;
        int bestCount = 0;
        for (int row = 0; row < matrix.Length; row++)
        {
            if (matrix[row].ToList().Count(c => c == 'W') > bestCount)
            {
                bestCount = matrix[row].ToList().Count(c => c == 'W');
                bestRow = row;
            }
        }
        return new Tuple<int, int>(bestRow, bestCount);
    }

    private static void InvertRow(int row, char[][] matrix)
    {
        for (int col = 0; col < matrix.Length; col++)
        {
            matrix[row][col] = matrix[row][col] == 'W' ? 'B' : 'W';
        }
    }

    private static void InvertCol(int col, char[][] matrix)
    {
        for (int row = 0; row < matrix.Length; row++)
        {
            matrix[row][col] = matrix[row][col] == 'W' ? 'B' : 'W';
        }
    }
}