#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));
auto odw = vector<vector<bool>> (n, vector<bool>(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;
}
}
vector<vector<int>> nq;
vector<vector<int>> q = {{0,0}}; // x, y
int maxi = 0;
bool a = true;
int iq=0, inq=0;
while(true) {
int ssiz = a ? q.size() : nq.size();
int cq = a ? iq : inq;
if(cq >= ssiz) break;
for(;cq<ssiz;cq++) {
auto cur = a ? q[cq] : nq[cq];
int x = cur[0], y = cur[1], 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(odw[ny][nx]) continue;
int nr = v[ny][nx];
if(nr == -1 * r) {
if(a) nq.push_back({nx, ny});
else q.push_back({nx, ny});
} else if(nr == r) {
if(a) q.push_back({nx, ny});
else nq.push_back({nx, ny});
ssiz++;
}
odw[ny][nx] = true;
}
}
if(a) iq = cq;
else inq = cq;
a = !a;
maxi++;
}
cout<<maxi<<'\n';
}
/*
5 8
FFR.....
.FRRR...
.FFFFF..
..RRRFFR
.....FFF
*/
