#include <bits/stdc++.h>
using namespace std;
int H,W;
void dfs(int r,int c,vector<vector<int>>& matrix,vector<vector<int>>& minDist){
// cout << r << " " << c << endl;
int dx[4] = {0,1,-1,0};
int dy[4] = {1,0,0,-1};
for(int i = 0;i < 4;i++){
int newX = r+dx[i];
int newY = c+dy[i];
if(newX < 0 || newY < 0 || newX >= H || newY >= W){
continue;
}
if(matrix[newX][newY] == 0)continue;
int newDist = minDist[r][c];
if(matrix[newX][newY] != matrix[r][c]){
newDist++;
}
if(minDist[newX][newY] > newDist){
minDist[newX][newY] = newDist;
dfs(newX,newY,matrix,minDist);
}
}
}
int main(){
cin.tie(0);
ios_base::sync_with_stdio(0);
//start here
cin >> H >> W;
vector<vector<int>> matrix(H,vector<int>(W,0));
for(int i = 0;i < H;i++){
for(int j = 0; j < W;j++){
char tmp;
cin >> tmp;
if(tmp == 'F'){
matrix[i][j] = 1;
}else if(tmp == 'R'){
matrix[i][j] = 2;
}
}
}
vector<vector<int>> min_dist(H,vector<int>(W,INT_MAX));
int ans = 0;
min_dist[0][0] = 1;
dfs(0,0,matrix,min_dist);
for(int i = 0; i < H;i++){
for(int j = 0; j < W;j++){
if(matrix[i][j] != 0){
ans = max(min_dist[i][j],ans);
// cout << min_dist[i][j] << " ";
}
// else{
// cout << 0 << " ";
// }
}
// cout << endl;
}
cout << ans;
}
