#include <bits/stdc++.h>
using namespace std;
#define pii pair<int,int>
int pole[4004][4004];
int dist[4004][4004];
bool vis[4004][4004];
int k_x[4]={-1,0,1,0};
int k_y[4]={0,-1,0,1};
deque<pii> dq;
int bfs01(){
int mx=0;
dq.push_back({1,1});
dist[1][1]=1;
vis[1][1]=true;
while(dq.size()){
pii now=dq.front();
dq.pop_front();
mx=max(mx,dist[now.first][now.second]);
for (int i = 0; i<4; i++){
if (pole[now.first+k_x[i]][now.second+k_y[i]] && !vis[now.first+k_x[i]][now.second+k_y[i]]){
if (pole[now.first+k_x[i]][now.second+k_y[i]]==pole[now.first][now.second]){
dist[now.first+k_x[i]][now.second+k_y[i]]=dist[now.first][now.second];
dq.push_front({now.first+k_x[i],now.second+k_y[i]});
}
else{
dist[now.first+k_x[i]][now.second+k_y[i]]=dist[now.first][now.second]+1;
dq.push_back({now.first+k_x[i],now.second+k_y[i]});
}
vis[now.first+k_x[i]][now.second+k_y[i]]=true;
}
}
}
return mx;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int n,m;
cin >> n >> m;
char zn;
for (int i = 1; i<=n; i++){
for (int j = 1; j<=m; j++){
cin >> zn;
if (zn=='R')pole[i][j]=1;
if (zn=='F')pole[i][j]=2;
}
}
cout << bfs01() << '\n';
}
