#include <bits/stdc++.h>
using namespace std;
int n, m;
vector<vector<int>> v;
vector<pair<int,int>> mv = {{0,1},{0,-1},{1,0},{-1,0}};
int main(){
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
cin>>n>>m;
v = vector<vector<int>> (n, vector<int>(m));
char c;
for(int i=0;i<n;i++){
for (int j = 0; j < m; ++j) {
cin>>c;
if(c=='R') v[i][j] = 1;
else if(c=='F') v[i][j] = -1;
}
}
priority_queue<vector<int>> q; // value, x, y
q.push({-1,0,0});
int maxi = 0;
while(!q.empty()) {
auto cur = q.top();
q.pop();
int val = cur[0], x= cur[1], y = cur[2], r = v[y][x];
if(r==0) continue;
for(auto &cm : mv) {
int nx = x + cm.first, ny = y + cm.second;
if(nx<0 || ny<0 || nx>=m || ny>=n) continue;
if(v[ny][nx] == -1 * r) {
maxi = max(maxi, -(val-1));
q.push({val-1, nx, ny});
} else if(v[ny][nx] == r) {
q.push({val, nx, ny});
}
}
v[y][x] = 0; //odw
}
cout<<maxi<<'\n';
}
/*
5 8
FFR.....
.FRRR...
.FFFFF..
..RRRFFR
.....FFF
*/
