#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> pii;
struct trio{
int val, x, y;
bool operator < (const trio& other)const{
return val < other.val;
}
};
const int N = 4003;
const vector<pii> DIR = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
char tab[N][N];
int dist[N][N];
bool vis[N][N];
priority_queue<trio> pq;
void solve(){
vis[1][1] = 1;
pq.push({0, 1, 1});
int x, y, xp, yp;
while(!pq.empty()){
x = pq.top().x;
y = pq.top().y;
pq.pop();
for(auto p : DIR){
xp = x + p.first;
yp = y + p.second;
if(vis[xp][yp]) continue;
if(tab[x][y] == tab[xp][yp]){
pq.push({-dist[x][y], xp, yp});
dist[xp][yp] = dist[x][y];
vis[xp][yp] = 1;
}else if(tab[xp][yp] == 'F' || tab[xp][yp] == 'R'){
dist[xp][yp] = dist[x][y] + 1;
vis[xp][yp] = 1;
pq.push({-dist[xp][yp], xp, yp});
}
}
}
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int h, w;
cin >> h >> w;
for(int i = 1 ; i <= h ; i++){
for(int j = 1 ; j <= w ; j++){
cin >> tab[i][j];
}
}
solve();
int ans = 0;
for(int i = 1 ; i <= h ; i++){
for(int j = 1 ; j <= w ; j++){
ans = max(ans, dist[i][j]);
}
}
cout << ans + 1 << '\n';
}
