/**
* Solution by 1egend (polarity.sh)
* Date: 2024-10-30
* Contest: BOI 2013
* Problem: tracks
**/
#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define ull unsigned long long
#define ll long long
const int MAX_N = 1e5 + 1;
const ll MOD = 1e9 + 7;
vector<pair<int, int>> cardinal = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
vector<vector<int>> grid;
vector<vector<int>> component;
void floodfill(int i, int j, int n, int l){
if (grid[i][j] != l || component[i][j] != 0){
return;
}
component[i][j] = n;
for (pair<int, int> t : cardinal){
floodfill(i + t.first, j + t.second, n, l);
}
}
void solve(){
int h, w; cin >> h >> w;
grid = vector<vector<int>>(h + 2, vector<int>(w + 2, 0));
component = grid;
for (int i = 0; i < h; i++){
string s; cin >> s;
for (int j = 0; j < w; j++){
char t = s[j];
if (t == 'F'){
grid[i + 1][j + 1] = 2;
} else if (t == 'R'){
grid[i + 1][j + 1] = 1;
}
}
}
int k = 1;
for (int i = 1; i < h + 1; i++){
for (int j = 1; j < w + 1; j++){
if (component[i][j] == 0 && grid[i][j] != 0){
floodfill(i, j, k, grid[i][j]);
k++;
}
}
}
vector<vector<int>> adj(k + 1);
for (int i = 1; i < h + 1; i++){
for (int j = 1; j < w + 1; j++){
int x = component[i][j];
for (pair<int, int> t : cardinal){
int y = component[i + t.first][j + t.second];
if (x != 0 && y != 0 && x != y){
adj[x].pb(y);
adj[y].pb(x);
}
}
}
}
vector<int> dist(k + 1, -1);
int ans = 0;
queue<int> curr;
curr.push(1);
dist[1] = 0;
while(!curr.empty()){
int comp = curr.front();
curr.pop();
for (int node : adj[comp]){
if (dist[node] != -1){
continue;
}
dist[node] = dist[comp] + 1;
ans = max(ans, dist[node]);
curr.push(node);
}
}
cout << ans + 1 << endl;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
solve();
return 0;
}
