#include <bits/stdc++.h>
using namespace std;
int H, W;
int grid[4001][4001], cc[4001][4001];
queue<pair<int,int>> q;
vector<pair<int,int>> dir = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
void ff(int cur, int val){
while(!q.empty()){
auto temp = q.front();
int x = temp.first, y = temp.second;
q.pop();
for(auto [dx, dy] : dir){
if((x+dx > -1)&& (x+dx < H) && (y+dy > -1) && (y+dy < W) && (cc[x+dx][y+dy] == -1) && (grid[x+dx][y+dy] == cur)){
cc[x+dx][y+dy] = val;
q.push({x+dx, y+dy});
}
}
}
}
int main(){
cin>>H>>W;
memset(grid, 0, sizeof(grid));
memset(cc, -1, sizeof(cc));
for(int i = 0; i < H; i++){
string s; cin>>s;
for(int j = 0; j < W; j++){
if(s[j] == 'F') grid[i][j] = 1;
else if(s[j] == 'R') grid[i][j] = 2;
}
}
int val = 0;
for(int i = 0; i < H; i++){
for(int j = 0; j < W; j++){
if(cc[i][j] == -1 && grid[i][j] != 0){
cc[i][j] = val;
q.push({i,j});
ff(grid[i][j], val);
val++;
}
}
}
vector<set<int>> adj(val+1);
for(int i = 0; i < H; i++){
for(int j = 0; j < W; j++){
if(grid[i][j] != 0){
for(auto [dx, dy] : dir){
if(i+dx > -1 && i+dx < H && j+dy > -1 && j+dy < W && grid[i+dx][j+dy] != grid[i][j] && grid[i+dx][j+dy] != 0){
adj[cc[i][j]].insert(cc[i+dx][j+dy]);
adj[cc[i+dx][j+dy]].insert(cc[i][j]);
}
}
}
}
}
queue<int> q1;
q1.push(0);
vector<int> v(val+1, 0), d(val+1, 0);
v[0] = 1;
int ans = 0;
while(!q1.empty()){
auto temp = q1.front();
q1.pop();
for(auto i : adj[temp]){
if(!v[i]){
q1.push(i);
v[i] = 1;
d[i] = d[temp] + 1;
ans = max(ans, d[i]);
}
}
}
cout<<ans+1<<endl;
return 0;
}
