#include <bits/stdc++.h>
using namespace std;
constexpr int INF = 1000000;
constexpr int MAXN = 4000;
int grid[MAXN][MAXN];
vector<vector<int>> component (MAXN, vector<int>(MAXN, -1));
set<int> adj[MAXN];
int num_components = 0;
int R, C;
void dfs(int r, int c, int num){
component[r][c] = num;
if(r>0){
if(grid[r-1][c] == grid[r][c] && component[r-1][c] == -1){
dfs(r-1, c, num);
}
if(grid[r-1][c] != grid[r][c] && component[r-1][c] != -1){
adj[num].insert(component[r-1][c]);
adj[component[r-1][c]].insert(num);
}
}
if(r<R-1){
if(grid[r+1][c] == grid[r][c] && component[r+1][c] == -1){
dfs(r+1, c, num);
}
if(grid[r+1][c] != grid[r][c] && component[r+1][c] != -1){
adj[num].insert(component[r+1][c]);
adj[component[r+1][c]].insert(num);
}
}
if(c>0){
if(grid[r][c-1] == grid[r][c] && component[r][c-1] == -1){
dfs(r, c-1, num);
}
if(grid[r][c-1] != grid[r][c] && component[r][c-1] != -1){
adj[num].insert(component[r][c-1]);
adj[component[r][c-1]].insert(num);
}
}
if(c<C-1){
if(grid[r][c+1] == grid[r][c] && component[r][c+1] == -1){
dfs(r, c+1, num);
}
if(grid[r][c+1] != grid[r][c] && component[r][c+1] != -1){
adj[num].insert(component[r][c+1]);
adj[component[r][c+1]].insert(num);
}
}
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> R >> C;
char a;
for(int r = 0; r != R; ++r){
for(int c = 0; c != C; ++c){
cin >> a;
if(a == '.') { grid[r][c] = 0; }
if(a == 'R') { grid[r][c] = 1; }
if(a == 'F') { grid[r][c] = 2; }
}
}
for(int r = 0; r != R; ++r){
for(int c = 0; c != C; ++c){
if(component[r][c] != -1) continue;
if(grid[r][c] == 0) continue;
dfs(r, c, num_components);
num_components++;
}
}
//bfs
vector<int> visited(num_components, INF);
queue<int> q;
q.push(0);
visited[0] = 1;
while(!q.empty()){
int x = q.front();
q.pop();
//process node
for(int e : adj[x]){
if(visited[e] != INF) continue;
q.push(e);
visited[e] = visited[x] + 1;
}
}
int result = 0;
for(int i = 0; i < num_components; ++i){
result = max(result, visited[i]);
}
cout << result;
return 0;
}
