#include <bits/stdc++.h>
using namespace std;
int main(){
int h,w;
cin >> h >> w;
vector<vector<int>> gr(h,vector<int>(w));
for(int i=0;i<h;i++){
string s;
cin >> s;
for(int j=0;j<w;j++){
if(s[j]=='R')gr[i][j]=1;
else if(s[j]=='F')gr[i][j]=-1;
}
}
deque<pair<int,int>> dq;
vector<vector<int>> dist(h,vector<int>(w));
dist[0][0]=1;
dq.push_front({0,0});
int ans=1;
while(!dq.empty()){
auto [i,j]=dq.front();
dq.pop_front();
ans=max(ans,dist[i][j]);
if(i>0 and dist[i-1][j]==0){
if(gr[i-1][j]==gr[i][j]){
dq.push_front({i-1,j});
dist[i-1][j]=dist[i][j];
}
else if(gr[i-1][j]*(-1)==gr[i][j]){
dq.push_back({i-1,j});
dist[i-1][j]=dist[i][j]+1;
}
}
if(i<h-1 and dist[i+1][j]==0){
if(gr[i+1][j]==gr[i][j]){
dq.push_front({i+1,j});
dist[i+1][j]=dist[i][j];
}
else if(gr[i+1][j]*(-1)==gr[i][j]){
dq.push_back({i+1,j});
dist[i+1][j]=dist[i][j]+1;
}
}
if(j>0 and dist[i][j-1]==0){
if(gr[i][j]==gr[i][j-1]){
dq.push_front({i,j-1});
dist[i][j-1]=dist[i][j];
}
else if(gr[i][j-1]*(-1)==gr[i][j]){
dq.push_back({i,j-1});
dist[i][j-1]=dist[i][j]+1;
}
}
if(j<w-1 and dist[i][j+1]==0){
if(gr[i][j]==gr[i][j+1]){
dq.push_front({i,j+1});
dist[i][j+1]=dist[i][j];
}
else if(gr[i][j+1]*(-1)==gr[i][j]){
dq.push_back({i,j+1});
dist[i][j+1]=dist[i][j]+1;
}
}
}
cout << ans << "\n";
}
