#include<bits/stdc++.h>

using namespace std;
const int N = 110;
#define x first
#define y second
typedef pair<int, int> PII;
int a[N][N];
int dx[] = {-1, 1, 0, 0};
int dy[] = {0, 0, -1, 1};

int n, m, Max;
vector<PII> s;

/**
测试数据
4 4
BLQB
BBQS
SBQL
QQQQ

输出
2

3 3
LSB
QBQ
BSL

输出
-1
 */

/**
 * 功能：深度优先搜索
 * @param x 横坐标
 * @param y 纵坐标
 * @param step 步数
 */
void dfs(int x, int y, int step) {
    //如果死循环，一直
    if (step > n * m) {
        cout << -1 << endl;
        exit(0);
    }
    //更新步数
    Max = max(Max, step);
    //4个方向
    for (int i = 0; i <= 3; i++) {
        int tx = x + dx[i];
        int ty = y + dy[i];
        //如果出界
        if (tx < 1 || tx > n || ty < 1 || ty > m) continue;
        //下一步与期望值对比
        if (a[tx][ty] == a[x][y] + 1 || (a[tx][ty] == 1 && a[x][y] == 4))
            dfs(tx, ty, step + 1);
    }
}

int main() {
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++) {
            char x;
            cin >> x;
            //记录起点
            if (x == 'L')
                a[i][j] = 1, s.push_back({i, j});
            else if (x == 'Q') a[i][j] = 2;
            else if (x == 'B') a[i][j] = 3;
            else if (x == 'S') a[i][j] = 4;
        }
    //模拟从每个起点开始
    for (int i = 0; i < s.size(); i++)
        dfs(s[i].x, s[i].y, 1);

    //长度除以4
    cout << Max / 4 << endl;
    return 0;
}