#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pll pair<ll, ll>
#define pii pair<int, int>
#define fs first
#define sc second
#define pb push_back
void solve() {
int n,m;
cin>>n>>m;
int a[n][m];
for(int i=0;i<n;i++){
for(int j=0;j<m;j++){
char c;
cin>>c;
if(c=='F')a[i][j]=0;
else if(c=='R')a[i][j]=1;
else a[i][j]=-1;
}
}
int dist[n][m],dx[4]={-1,1,0,0},dy[4]={0,0,-1,1},ans=0;
memset(dist,-1,sizeof(dist));
deque<pii> dq;
dist[0][0]=0;
dq.push_back({0,0});
while(!dq.empty()){
auto[r,c]=dq.front();
dq.pop_front();
for(int i=0;i<4;i++){
int r2=r+dx[i],c2=c+dy[i];
if(r2>=0&&c2>=0&&r2<n&&c2<m){
if(a[r2][c2]==-1||dist[r2][c2]!=-1)continue;
if(a[r2][c2]==a[r][c]){
dist[r2][c2]=dist[r][c];
dq.push_front({r2,c2});
}else{
dist[r2][c2]=dist[r][c]+1;
ans=max(ans,dist[r2][c2]);
dq.push_back({r2,c2});
}
}
}
a[r][c]=-1;
}
cout<<ans+1;
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
solve();
}
