#include <bits/stdc++.h>
using namespace std;
#define darvem ios_base::sync_with_stdio(false);cin.tie(NULL)
#define endl '\n'
#define ll long long
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
char animal[] = {'F', 'R'};
signed main(){
darvem;
int h, w;
cin >> h >> w;
vector<vector<char>> grid(h, vector<char>(w));
vector<vector<int>> visited(h, vector<int>(w));
for(int i = 0; i < h; i++) for(int j = 0; j < w; j++) cin >> grid[i][j];
queue<tuple<int, int, int>> p, q;
p.push({0, 0, 1});
int ans = 0;
int curr = grid[0][0] == 'R';
while(!(p.empty() && q.empty())){
if(p.empty()){
swap(p, q);
curr ^= 1;
}
auto [x, y, w] = p.front(); p.pop();
if(visited[x][y]) continue;
visited[x][y] = 1;
ans = max(ans, w);
for(int i = 0; i < 4; i++){
int a = x + dx[i], b= y + dy[i];
if(a < 0 or b < 0 or a == h or b == w) continue;
if(grid[a][b] == animal[curr]) p.push({a, b, w});
else if(grid[a][b] != '.') q.push({a, b, w+1});
}
}
cout << ans << endl;
}
