#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> pi;
#define mp make_pair
#define f first
#define s second
#define sz(x) (int)(x).size()
int xd[4] = {1, 0, -1, 0};
int yd[4] = {0, 1, 0, -1};
const int MOD = 1e9+7;
int grid[4005][4005];
int dist[4005][4005];
int ans = 1;
int main(){
int H, W;
cin >> H >> W;
for(int i = 1; i <= H; i++){
string s;
cin >> s;
for(int j = 0; j < W; j++){
if(s[j] == 'R'){
grid[i][j+1] = 1;
}
else if(s[j] == 'F'){
grid[i][j+1] = 2;
}
}
}
for(int i = 1; i <= H; i++){
for(int j = 1; j <= W; j++){
dist[i][j] = MOD;
}
}
queue<pi> q; //have ans value
queue<pi> nq;
dist[1][1] = 1;
q.push(mp(1, 1));
while(sz(q)){
pi co = q.front();
q.pop();
//cout << co.f << " " << co.s << "\n";
for(int d = 0; d < 4; d++){
int x = co.f+xd[d];
int y = co.s+yd[d];
if(grid[x][y] == 0) continue;
if(dist[x][y] != MOD) continue;
//cout << "x y: " << x << " " << y << "\n";
if(grid[x][y] == grid[co.f][co.s]){
dist[x][y] = ans;
q.push(mp(x, y));
}
else{
dist[x][y] = ans+1;
nq.push(mp(x, y));
}
}
if(sz(q) == 0){
if(sz(nq) == 0) break;
swap(nq, q);
//cout << "AD" << "\n";
ans++;
}
}
cout << ans << "\n";
}
