#include <bits/stdc++.h>
using namespace std;
const int N=4e3+5;
int di[4]={1,-1,0,0};
int dj[4]={0,0,1,-1};
int n,m,ans;
int8_t v[N][N];
int check(int i, int j){
return 0<=i && i<n && 0<=j && j<m && v[i][j]!=-1;
}
bool vis[N][N];
int main()
{
memset(v, -1, sizeof(v));
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin>>n>>m;
for (int i=0;i<n;i++){
for (int j=0;j<m;j++){
char c;cin>>c;
if (c=='F'){
v[i][j]=1;
}
else if(c=='R'){
v[i][j]=0;
}
}
}
deque<tuple<int, int, int, int>>q;
q.push_front(make_tuple(0,0,0,v[0][0]));
while (!q.empty()){
auto x=q.front();
q.pop_front();
int i=get<0>(x);
int j=get<1>(x);
int cd=get<2>(x);
int animal=get<3>(x);
ans=max(ans, cd+1);
for (int k=0;k<4;k++){
int newi=i+di[k];
int newj=j+dj[k];
if (check(newi, newj) && !vis[newi][newj]){
if (animal==v[newi][newj]){
//same animal -> to the front of the queue
vis[newi][newj]=true;
q.push_front(make_tuple(newi, newj, cd, v[newi][newj]));
}
else{
//different animal -> to the back of the queue
vis[newi][newj]=true;
q.push_back(make_tuple(newi, newj, cd+1, v[newi][newj]));
}
}
}
}
cout<<ans;
return 0;
}
