#include <bits/stdc++.h>
using namespace std;
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};
int main(){
ios::sync_with_stdio(false);
cin.tie(0);
int n, m;
cin >> n >> m;
char graph[n][m];
for (int i = 0; i < n; i ++) for (int j = 0; j < m; j ++) cin >> graph[i][j];
int cnt[n][m];
int inf = 0x3f3f3f3f;
memset(cnt, inf, sizeof(cnt));
cnt[0][0] = 1;
deque<pair<int, int> > que;
que.push_front(make_pair(0, 0));
while(! que.empty()){
pair<int, int> p = que.front();
que.pop_front();
for (int i = 0; i < 4; i ++){
int x = p.first + dx[i];
int y = p.second + dy[i];
if (x >= 0 && x < n && y >= 0 && y < m && cnt[x][y] > cnt[p.first][p.second] + (graph[x][y] != graph[p.first][p.second]) && (graph[x][y] == 'R' || graph[x][y] == 'F')){
if (graph[x][y] != graph[p.first][p.second]){
cnt[x][y] = cnt[p.first][p.second] + 1;
que.push_back(make_pair(x, y));
} else{
cnt[x][y] = cnt[p.first][p.second];
que.push_front(make_pair(x, y));
}
}
}
}
int ans = 0;
for (int i = 0; i < n; i ++){
for (int j = 0; j < m; j ++) if (cnt[i][j] != inf) ans = max(ans, cnt[i][j]);
}
cout << ans << endl;
}
