#include <bits/stdc++.h>
#define int long long
#define SETIO cin.tie(0);cout.tie(0);ios_base::sync_with_stdio(false);
#define REP(i,a,b)for(int i=a;i<b;i++)
#define fi first
#define se second
#define pb push_back
#define FORI(v)for(auto i:v)
#define FORJ(v)for(auto j:v)
using namespace std;
using pii=pair<int, int>;
int color[5000][5000];
bool visited[5000][5000];
int w, h;
int bfs(){
deque<pair<pii, int>> q;
q.pb({{0,0},1});
int ans=1;
while(q.size()){
auto qt = q.front();q.pop_front();
auto top = qt.fi;
if(top.fi<0)continue;
if(top.fi>=h)continue;
if(top.se<0)continue;
if(top.se>=w)continue;
if(visited[top.fi][top.se])continue;
visited[top.fi][top.se]=true;
int cur=color[top.fi][top.se];
if(cur==0)continue;
#define PUSH(x, y) if(cur!=color[x][y])q.pb({{x,y},qt.se+1});else q.push_front({{x,y},qt.se});
PUSH(top.fi+1,top.se);
PUSH(top.fi-1,top.se);
PUSH(top.fi,top.se+1);
PUSH(top.fi,top.se-1);
ans=max(ans,qt.se);
}
return ans;
}
#undef int
int main() {
#define int long long
SETIO;
cin>>h>>w;
REP(i,0,h){
REP(j,0,w){
char c;cin>>c;
if(c=='.')color[i][j]=0;
if(c=='R')color[i][j]=1;
if(c=='F')color[i][j]=2;
}
}
memset(visited,0,sizeof visited);
cout<<bfs()<<endl;
}
