#include <iostream>

#include <cmath>

#include <queue>

using namespace std;

string board[50];

bool visited[50][50];

int N, M;

int dx[4] = {0, 0, 1, -1};

int dy[4] = {1, -1, 0, 0};

int getmaxd(int i, int j)

{

int res = 0;

visited[i][j] = true;

queue<pair<pair<int, int>, int>> bfsQueue;

bfsQueue.push({{i, j}, 0});

while (!bfsQueue.empty())

{

int x = bfsQueue.front().first.first;

int y = bfsQueue.front().first.second;

int d = bfsQueue.front().second;

res = max(res, d);

bfsQueue.pop();

for (int t = 0; t < 4; t++)

{

int tx = x + dx[t];

int ty = y + dy[t];

if (tx >= 0 && ty >= 0 && tx < N && ty < M && !visited[tx][ty] && board[tx][ty] == 'L')

{

visited[tx][ty] = true;

bfsQueue.push({{tx, ty}, d + 1});

}

}

}

return res;

}

void reservisited()

{

for (int i = 0; i < N; i++)

{

for (int j = 0; j < M; j++)

{

visited[i][j] = false;

}

}

}

int main()

{

ios::sync_with_stdio(0);

cin.tie(0);

cin >> N >> M;

int i, j;

int ans = 0;

for (i = 0; i < N; i++)

{

cin >> board[i];

}

for (i = 0; i < N; i++)

{

for (j = 0; j < M; j++)

{

if (board[i][j] == 'L')

{

reservisited();

ans = max(ans, getmaxd(i, j));

}

}

}

cout << ans << "\n";

return 0;

}