#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 id[4010][4010],a[4010][4010],cnt=0,x,y,h,w,i,j;
char c;
vector<pll> adj[7*1000010];
int d[7*1000010];
bool visited[7*1000010];
priority_queue<pll,vector<pll>,greater<pll>> pq;
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;
id[i][j]=++cnt;
}
else if (c=='F'){
a[i][j]=2;
id[i][j]=++cnt;
}
else a[i][j]=0;
}
}
for (i=1;i<=h;i++){
for (j=1;j<=w;j++){
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;
if (a[i][j]==a[x][y]){
adj[id[i][j]].push_back({0,id[x][y]});
adj[id[x][y]].push_back({0,id[i][j]});
}
else{
adj[id[i][j]].push_back({1,id[x][y]});
adj[id[x][y]].push_back({1,id[i][j]});
}
}
}
}
for (i=1;i<=cnt;i++) d[i]=1e9;
d[1]=0;
pq.push({0,1});
while (!pq.empty()){
int u=pq.top().second;
pq.pop();
if (visited[u]) continue;
visited[u]=1;
for (auto pr:adj[u]){
int w=pr.first,v=pr.second;
if (d[v]>d[u]+w){
d[v]=d[u]+w;
pq.push({d[v],v});
}
}
}
int ans=0;
for (i=1;i<=cnt;i++){
if (d[i]<1e9) ans=max(ans,d[i]);
}
cout<<ans+1;
}
