#include <bits/stdc++.h>
#define fr first
#define se second
#define rep(i,a,b) for(int i = a; i < (b); ++i)
#define repr(i,a,b) for(int i = a; i > (b); --i)
#define sz(x) (int)(x).size()
#define all(x) (x).begin(),(x).end()
#define IN(i,l,r) (l<i&&i<r)
#define pb push_back
#define dbg(v) \
cout << "Line(" << __LINE__ << ") -> " << #v << " = " << (v) << endl;
using namespace std;
typedef pair<int,int> pi;
typedef vector<int> vi;
typedef long long ll;
int h,w;
const int U = 4002;
int grid[U][U],dist[U][U];
int dx[4] = {0,0,-1,1};
int dy[4] = {-1,1,0,0};
bool valid(int x,int y){
return IN(x,-1,h) && IN(y,-1,w) && grid[x][y]!=1;
}
int main(){
cin.tie(0)->sync_with_stdio(false);
cin >> h >> w;
rep(i,0,h){
rep(j,0,w){
char x; cin >> x;
if(x=='.') grid[i][j]=1;
else if(x=='F') grid[i][j]=2;
else if(x=='R') grid[i][j]=3;
}
}
deque<pair<int,int>> q;
q.push_back({0,0});
dist[0][0] = 1;
while(q.size()){
pi c = q.front(); q.pop_front();
rep(k,0,4){
int x = c.fr+dx[k],y = c.se+dy[k];
if(valid(x,y) && dist[x][y] == 0){
if(grid[x][y] == grid[c.fr][c.se]){
dist[x][y] = dist[c.fr][c.se];
q.push_front({x,y});
}else{
dist[x][y] = dist[c.fr][c.se]+1;
q.push_back({x,y});
}
}
}
}
int ans = 1;
rep(i,0,h)
rep(j,0,w) ans = max(ans,dist[i][j]);
cout << ans << '\n';
}
