#include <bits/stdc++.h>
#define ff first
#define ss second
#define endl '\n'
using namespace std;
const long long INF = (long long) 1e18;
const int mod = (int) 1e9+7;
const int MAXN = (int) 4e3+5;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
int h, w;
char g[MAXN][MAXN];
int dx[] = {-1, 0, 0, 1};
int dy[] = {0, -1, 1, 0};
bool vis[MAXN][MAXN];
queue<pii> rab, fox;
bool ic(int x, int y){
return (x >= 0 && x < h && y >= 0 && y < w);
}
int rb();
int fx(){
if(fox.empty()) return 0;
while(!fox.empty()){
pii cur = fox.front();
fox.pop();
for(int j = 0; j < 4; j++){
int nx = cur.ff + dx[j], ny = cur.ss + dy[j];
if(!ic(nx, ny)) continue;
if(g[nx][ny] == 'R' && vis[nx][ny] == 0){
vis[nx][ny] = 1;
rab.push({nx, ny});
}else if(g[nx][ny] == 'F' && vis[nx][ny] == 0){
vis[nx][ny] = 1;
fox.push({nx, ny});
}
}
}
return 1 + rb();
}
int rb(){
if(rab.empty()) return 0;
while(!rab.empty()){
pii cur = rab.front();
rab.pop();
for(int j = 0; j < 4; j++){
int nx = cur.ff + dx[j], ny = cur.ss + dy[j];
if(!ic(nx, ny)) continue;
if(g[nx][ny] == 'F' && vis[nx][ny] == 0){
vis[nx][ny] = 1;
fox.push({nx, ny});
}else if(g[nx][ny] == 'R'&& vis[nx][ny] == 0){
vis[nx][ny] = 1;
rab.push({nx, ny});
}
}
}
return 1 + fx();
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);cout.tie(nullptr);
#ifdef Local
freopen("C:/Users/Admin/Desktop/Yazilim/C/IO/int.txt","r",stdin);
freopen("C:/Users/Admin/Desktop/Yazilim/C/IO/out.txt","w",stdout);
#endif
cin>>h>>w;
for(int i = 0; i < h; i++) cin>>g[i];
assert(g[0][0] == g[h - 1][w - 1]);
vis[0][0] = 1;
if(g[0][0] == 'F'){
fox.push({0, 0});
cout<<fx()<<endl;
}else{
rab.push({0, 0});
cout<<rb()<<endl;
}
#ifdef Local
cout<<endl<<fixed<<setprecision(2)<<1000.0 * clock() / CLOCKS_PER_SEC<< " milliseconds ";
#endif
}
