#include<bits/stdc++.h>
#define pll pair<int,int>
using namespace std;
const int dx[4]={1,-1,0,0};
const int dy[4]={0,0,-1,1};
int a[4001][4001],cnt=0,x,y,h,w,i,j;
char c;
int d[4001][4001];
bool visited[4001][4001];
deque<pll> dq;
signed main(){
cin.tie(0)->sync_with_stdio(0);
cin>>h>>w;
for (i=1;i<=h;i++){
for (j=1;j<=w;j++){
cin>>c;
if (c=='R'){
a[i][j]=1;
}
else if (c=='F'){
a[i][j]=2;
}
else a[i][j]=0;
d[i][j]=1e9;
}
}
d[1][1]=0;
dq.push_front({1,1});
while (!dq.empty()){
auto [i,j]=dq.front();
dq.pop_front();
if (visited[i][j]) continue;
visited[i][j]=1;
for (int k=0;k<4;k++){
x=dx[k]+i;y=dy[k]+j;
if (x<0||y<0||x>h||y>w) continue;
if (a[i][j]==0||a[x][y]==0) continue;
int w;
if (a[i][j]==a[x][y]) w=0;
else w=1;
if (d[x][y]>d[i][j]+w){
d[x][y]=d[i][j]+w;
if (w==0) dq.push_front({x,y});
else dq.push_back({x,y});
}
}
}
int ans=0;
for (i=1;i<=h;i++){
for (j=1;j<=w;j++){
if (d[i][j]<1e9) ans=max(ans,d[i][j]);
}
}
cout<<ans+1;
}
