#include "bits/stdc++.h"
using namespace std;
const int N=4000;
int n, m;
short dx[]={0, 0, 1, -1};
short dy[]={1, -1, 0, 0};
vector<int> adj[N*N];
short grid[N][N];
int cmp[N][N];
int vis[N*N];
void dfs(int u, int c){
cmp[u/m][u%m]=c;
int i=u/m;
int j=u%m;
for(int k=0; k<4; k++){
int x=i+dx[k];
int y=j+dy[k];
if(x<0 || x==n || y<0 || y==m || grid[x][y]!=grid[i][j] || cmp[x][y]) continue;
dfs(m*x+y, c);
}
}
int main(){
cin.tie(0)->sync_with_stdio(0);
cin >> n >> m;
for(int i=0; i<n; i++){
for(int j=0; j<m; j++){
char c; cin >> c;
grid[i][j]=(c=='F'?2:c=='R'?1:0);
}
}
int c=0;
for(int i=0; i<n; i++){
for(int j=0; j<m; j++){
if(grid[i][j]==0 || cmp[i][j]) continue;
dfs(m*i+j, ++c);
}
}
for(int i=0; i<n; i++){
for(int j=0; j<m; j++){
if(grid[i][j]==0) continue;
for(int k=0; k<4; k++){
int x=i+dx[k];
int y=j+dy[k];
if(x<0 || x==n || y<0 || y==m || grid[x][y]==grid[i][j] || grid[x][y]==0) continue;
adj[cmp[i][j]].push_back(cmp[x][y]);
adj[cmp[x][y]].push_back(cmp[i][j]);
}
}
}
for(int i=1; i<=c; i++){
sort(adj[i].begin(), adj[i].end());
adj[i].erase(unique(adj[i].begin(), adj[i].end()), adj[i].end());
}
queue<int> q;
int r=cmp[0][0];
q.push(r);
for(; !q.empty(); q.pop()){
int x=q.front();
for(int k:adj[x]){
if(!vis[k] && k!=r){
vis[k]=vis[x]+1;
q.push(k);
}
}
}
int mx=0;
for(int i=1; i<=c; i++) mx=max(mx, vis[i]);
cout << mx+1;
}
// when its been a long time since goodbye
