#include <bits/stdc++.h>
using namespace std;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int row, col;
cin>>row>>col;
char meadow[row][col];
int vis[row][col];
for(int i=0;i<row;i++){
fill(vis[i],vis[i]+col,0);
}
for(int i=0;i<row;i++){
for(int j=0;j<col;j++){
cin>>meadow[i][j];
}
}
int numberoftimes=0;
if(meadow[0][0]=='.')return 0;
int dx[4] = {0, 0, -1, 1},dy[4] = {1, -1, 0, 0}; //dx and dy stores the way to get to the adjacent nodes
vis[0][0]=1;
queue<tuple<int, int,int,char> > q; //pair contains <y_coord, x_coord>
q.push(make_tuple(0, 0,1,meadow[0][0])); //push the starting node
while (!q.empty()) {
int y = get<0>(q.front());
int x = get<1>(q.front());
int number = get<2>(q.front());
char currchar = get<3>(q.front());
q.pop();
for (int i = 0; i < 4; i++) {
int new_y = y + dy[i], new_x = x + dx[i]; //adjacent nodes
if(new_y>=0 and new_y<row and new_x>=0 and new_x<col and (meadow[new_y][new_x]=='F' or meadow[new_y][new_x]=='R')){
if(vis[new_y][new_x]==0){
if(meadow[new_y][new_x]!=currchar){
vis[new_y][new_x]=number+1;
q.push(make_tuple(new_y,new_x,number+1,meadow[new_y][new_x]));
//if(new_y==2 and new_x==1)cout<<"FUCK OFF";
//if(new_y==3 and new_x==7)cout<<"HI"<<number;
}
else{
vis[new_y][new_x]=number;
q.push(make_tuple(new_y,new_x,number,meadow[new_y][new_x]));
}
}
else if(meadow[new_y][new_x]==currchar and vis[new_y][new_x]>number){
vis[new_y][new_x]=number;
q.push(make_tuple(new_y,new_x,number,meadow[new_y][new_x]));
}
else if(meadow[new_y][new_x]!=currchar and vis[new_y][new_x]>number+1){
vis[new_y][new_x]=number+1;
q.push(make_tuple(new_y,new_x,number+1,meadow[new_y][new_x]));
}
}
//check if new node is within bounds, not visited and reachable (code for if it is not)
}
//cout<<"y: "<<y<<" x: "<<x<<" vis: "<<vis[y][x]<<" currchar: "<<currchar<<" number: "<<number<<"\n";
}
/*
for(int i=0;i<row;i++){
for(int j=0;j<col;j++){
cout<<vis[i][j]<<" ";
}
cout<<"\n";
}
*/
int maxx=-1;
for(int i=0;i<row;i++){
for(int j=0;j<col;j++){
maxx=max(maxx,vis[i][j]);
}
//cout<<"\n";
}
cout<<maxx;
}
/*
for(int i=0;i<row;i++){
for(int j=0;j<col;j++){
cout<<vis[i][j]<<" ";
}
cout<<"\n";
}
*/
//cout<<numberoftimes;
