#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
int mat[4005][4005];
int n, m;
int mx = 0;
int dist[4005][4005];
void bfs(){
deque <pair <int, int>> q;
q.push_front({1, 1});
for(int i=0; i<=n+1; i++){
for(int j=0; j<=m+1; j++){
dist[i][j] = 1000000000;
if(mat[i][j] == 0) dist[i][j] = -500;
}
}
dist[1][1] = 0;
while(!q.empty()){
pair <int, int> p = q.front();
q.pop_front();
int i = p.first;
int j = p.second;
mx = max(mx, dist[i][j]);
if(mat[i-1][j] == mat[i][j]){
if(dist[i][j] < dist[i-1][j]){
dist[i-1][j] = dist[i][j];
q.push_front({i-1, j});
}
}
else{
if(dist[i][j] + 1 < dist[i-1][j]){
dist[i-1][j] = dist[i][j] + 1;
q.push_back({i-1, j});
}
}
if(mat[i+1][j] == mat[i][j]){
if(dist[i][j] < dist[i+1][j]){
dist[i+1][j] = dist[i][j];
q.push_front({i+1, j});
}
}
else{
if(dist[i][j] + 1 < dist[i+1][j]){
dist[i+1][j] = dist[i][j] + 1;
q.push_back({i+1, j});
}
}
if(mat[i][j-1] == mat[i][j]){
if(dist[i][j] < dist[i][j-1]){
dist[i][j-1] = dist[i][j];
q.push_front({i, j-1});
}
}
else{
if(dist[i][j] + 1 < dist[i][j-1]){
dist[i][j-1] = dist[i][j] + 1;
q.push_back({i, j-1});
}
}
if(mat[i][j] == mat[i][j+1]){
if(dist[i][j] < dist[i][j+1]){
dist[i][j+1] = dist[i][j];
q.push_front({i, j+1});
}
}
else{
if(dist[i][j] + 1 < dist[i][j+1]){
dist[i][j+1] = dist[i][j] + 1;
q.push_back({i, j+1});
}
}
}
}
int main(){
ios_base::sync_with_stdio(false);
cout.precision(10);
cout<<fixed;
cin >> n >> m;
for(int i=1; i<=n; i++){
string s;
cin >> s;
for(int j=1; j<=m; j++){
if(s[j-1] == 'R') mat[i][j] = 1;
else if(s[j-1] == 'F') mat[i][j] = -1;
}
}
bfs();
cout << mx+1 << "\n";
return 0;
}
