#include <bits/stdc++.h>
using namespace std;
#define int long long
#define sp << " " <<
#define nl << "\n"
vector<int> e;
int find(int u){
return e[u] < 0 ? u : e[u] = find(e[u]);
}
void unite(int u, int v){
u = find(u), v = find(v);
if(u==v) return;
if(e[u] > e[v]) swap(u, v);
e[u] += e[v], e[v] = u;
}
int dx[4] = {-1, 1, 0, 0};
int dy[4] = {0, 0, -1, 1};
signed main(){
cin.tie(0)->sync_with_stdio(0);
int h, w; cin >> h >> w;
int g[h][w];
bool vis[h][w];
e.assign(h*w, -1);
queue<array<int, 3>> q;
for(int i=0; i<h; ++i){
for(int j=0; j<w; ++j){
char c; cin >> c;
if(c=='.') g[i][j] = 0;
if(c=='F') g[i][j] = 1;
if(c=='R') g[i][j] = 2;
if(i and g[i-1][j]==g[i][j]) unite(i*w + j, i*w + j - w);
if(j and g[i][j-1]==g[i][j]) unite(i*w + j, i*w + j - 1);
vis[i][j] = false;
}
}
for(int i=0; i<h; ++i){
for(int j=0; j<w; ++j){
if(find(i*w + j)==find(0)) q.push({i, j, 1}), vis[i][j] = true;
}
}
int ans = 0;
while(!q.empty()){
int x = q.front()[0], y = q.front()[1], d = q.front()[2]; q.pop();
for(int k=0; k<4; ++k){
int i = x + dx[k], j = y + dy[k];
if(i>=0 and j>=0 and i!=h and j!=w and g[i][j]==3-g[x][y] and !vis[i][j]){
q.push({i, j, d+1});
vis[i][j] = true;
}
}
ans = max(ans, d);
}
cout << ans;
}
