#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll mod = 1000000007;
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
int h,w;
cin >> h >> w;
int field[h][w];
for(int i = 0; i < h; i++) {
string s;
cin >> s;
for(int j = 0; j < w; j++) {
if(s[j]=='F') {
field[i][j]=1;
} else if(s[j]=='R') {
field[i][j]=2;
} else {
field[i][j]=0;
}
}
}
deque<pair<int, int>> q;
q.push_back({0,0});
vector<vector<int>> dist(h, vector<int>(w, -1));
dist[0][0]=1;
int ans = 1;
vector<int> dx{-1, 1, 0, 0}, dy{0,0,-1,1};
while(q.size()) {
pair<int, int> p = q.front();
q.pop_front();
for(int i = 0; i < 4; i++) {
int newx = p.first+dx[i];
int newy = p.second+dy[i];
if(newx>=0&&newy>=0&&newx<h&&newy<w&&field[newx][newy]!=0&&dist[newx][newy]==-1) {
if(field[newx][newy]==field[p.first][p.second]) {
dist[newx][newy]=dist[p.first][p.second];
q.push_front({newx, newy});
} else {
dist[newx][newy]=dist[p.first][p.second]+1;
q.push_back({newx, newy});
}
ans = max(ans, dist[newx][newy]);
}
}
}
cout << ans << endl;
}
