import java.util.*;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		char[][] board = new char[n][m];
		for (int a = 0; a < n; a++) {
			String s = sc.next();
			for (int b = 0; b < m; b++) {
				board[a][b] = s.charAt(b);
			}
		}
		int answer = 11;
		int count = 1;
		answer = Math.min(answer, left(count, board, n, m));
		answer = Math.min(answer, right(count, board, n, m));
		answer = Math.min(answer, up(count, board, n, m));
		answer = Math.min(answer, down(count, board, n, m));
		if (answer == 11) {
			System.out.println(-1);
		} else {
			System.out.println(answer);
		}
		sc.close();
	}

	private static int up(int count, char[][] board, int n, int m) {
		char[][] newboard = new char[n][m];
		for (int f = 0; f < n; f++) {
			for (int g = 0; g < m; g++) {
				newboard[f][g] = board[f][g];
			}
		}
		boolean candidate = false;
		if (count == 11) {
			return count;
		} else {
			for (int a = 1; a < n - 1; a++) {
				for (int b = 1; b < m - 1; b++) {
					if (newboard[a][b] == 'R' || newboard[a][b] == 'B') {
						char ch = newboard[a][b];
						for (int c = a - 1; c >= 0; c--) {
							if (newboard[c][b] == 'O') {
								if (ch == 'B') {
									return 11;
								} else {
									candidate = true;
									newboard[a][b] = '.';
									break;
								}
							} else if (newboard[c][b] != '.') {
								char temp = newboard[c + 1][b];
								newboard[c + 1][b] = newboard[a][b];
								newboard[a][b] = temp;
								break;
							}
						}
					}
				}
			}
		}
		if (candidate) {
			return count;
		} else {
			return Math.min(left(count + 1, newboard, n, m), right(count + 1, newboard, n, m));
		}
	}

	private static int down(int count, char[][] board, int n, int m) {
		char[][] newboard = new char[n][m];
		for (int f = 0; f < n; f++) {
			for (int g = 0; g < m; g++) {
				newboard[f][g] = board[f][g];
			}
		}
		boolean candidate = false;
		if (count == 11) {
			return count;
		} else {
			for (int a = n - 2; a > 0; a--) {
				for (int b = 1; b < m - 1; b++) {
					if (newboard[a][b] == 'R' || newboard[a][b] == 'B') {
						char ch = newboard[a][b];
						for (int c = a + 1; c < n; c++) {
							if (newboard[c][b] == 'O') {
								if (ch == 'B') {
									return 11;
								} else {
									candidate = true;
									newboard[a][b] = '.';
									break;
								}
							} else if (newboard[c][b] != '.') {
								char temp = newboard[c - 1][b];
								newboard[c - 1][b] = newboard[a][b];
								newboard[a][b] = temp;
								break;
							}
						}
					}
				}
			}
		}
		if (candidate) {
			return count;
		} else {
			return Math.min(left(count + 1, newboard, n, m), right(count + 1, newboard, n, m));
		}
	}

	private static int right(int count, char[][] board, int n, int m) {
		char[][] newboard = new char[n][m];
		for (int f = 0; f < n; f++) {
			for (int g = 0; g < m; g++) {
				newboard[f][g] = board[f][g];
			}
		}
		boolean candidate = false;
		if (count == 11) {
			return count;
		} else {
			for (int a = 1; a < n - 1; a++) {
				for (int b = m - 2; b > 0; b--) {
					if (newboard[a][b] == 'R' || newboard[a][b] == 'B') {
						char ch = newboard[a][b];
						for (int c = b + 1; c < m; c++) {
							if (newboard[a][c] == 'O') {
								if (ch == 'B') {
									return 11;
								} else {
									candidate = true;
									newboard[a][b] = '.';
									break;
								}
							} else if (newboard[a][c] != '.') {
								char temp = newboard[a][c - 1];
								newboard[a][c - 1] = newboard[a][b];
								newboard[a][b] = temp;
								break;
							}
						}
					}
				}
			}
		}
		if (candidate) {
			return count;
		} else {
			return Math.min(up(count + 1, newboard, n, m), down(count + 1, newboard, n, m));
		}
	}

	private static int left(int count, char[][] board, int n, int m) {
		char[][] newboard = new char[n][m];
		for (int f = 0; f < n; f++) {
			for (int g = 0; g < m; g++) {
				newboard[f][g] = board[f][g];
			}
		}
		boolean candidate = false;
		if (count == 11) {
			return count;
		} else {
			for (int a = 1; a < n - 1; a++) {
				for (int b = 1; b < m - 1; b++) {
					if (newboard[a][b] == 'R' || newboard[a][b] == 'B') {
						char ch = newboard[a][b];
						for (int c = b - 1; c >= 0; c--) {
							if (newboard[a][c] == 'O') {
								if (ch == 'B') {
									return 11;
								} else {
									candidate = true;
									newboard[a][b] = '.';
									break;
								}
							} else if (newboard[a][c] != '.') {
								char temp = newboard[a][c + 1];
								newboard[a][c + 1] = newboard[a][b];
								newboard[a][b] = temp;
								break;
							}
						}
					}
				}
			}
		}
		if (candidate) {
			return count;
		} else {
			return Math.min(up(count + 1, newboard, n, m), down(count + 1, newboard, n, m));
		}
	}
}