//
// Created by adavy on 1/31/2023.
//
// My Header
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using db = double;
using str = string; // yay python!
using ii = pair<int,int>;
using pl = pair<ll,ll>;
using pd = pair<db,db>;
using vi = vector<int>;
using vb = vector<bool>;
using vl = vector<ll>;
using vd = vector<db>;
using vs = vector<str>;
using vii = vector<ii>;
using vpl = vector<pl>;
using vpd = vector<pd>;
#define tcT template<class T
#define tcTU tcT, class U
tcT> using V = vector<T>;
tcT, size_t SZ> using AR = array<T,SZ>;
tcT> using PR = pair<T,T>;
// pairs
#define mp make_pair
#define f first
#define s second
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)
#define len(x) int((x).size())
#define bg(x) begin(x)
#define all(x) bg(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define sor(x) sort(all(x))
#define rsz resize
#define ins insert
#define ft front()
#define bk back()
#define pb push_back
#define eb emplace_back
#define pf push_front
const int MOD = 1e9+7; // 998244353;
const int MX = 2e5+5;
const ll INF = 1e18; // not too close to LLONG_MAX
const ld PI = acos((ld)-1);
const int dx[4] = {1,0,-1,0}, dy[4] = {0,1,0,-1}; // for every grid problem!!
int main(){
// 0-1 bfs
int H, W; cin >> H >> W;
vector<vi> grid;
F0R(i, H){
string row; cin >> row;
vector<int> x;
trav(c, row){
if (c=='R') x.pb(1);
else if (c=='F') x.pb(-1);
else x.pb(0);
}
grid.pb(x);
}
vector<vector<bool>> vis(H,vb(W,0));
vector<vector<int>> dist(H,vi(W));
deque<ii> q;
q.push_back({0,0});
dist[0][0] = 1; // H, W
vis[0][0] = 1;
int ans = 1;
while(q.size()){
auto [x, y] = q.front(); q.pop_front();
ans = max(ans, dist[x][y]);
F0R(d, 4){
int nx = x+dx[d], ny = y+dy[d];
if(!(0<=nx && nx<H && 0<=ny && ny<W)) continue;
if (vis[nx][ny]) continue;
if (grid[nx][ny]==0) continue;
vis[nx][ny] = 1;
if (grid[nx][ny]==grid[x][y]){
q.push_front({nx,ny});
dist[nx][ny] = dist[x][y];
}
else if (grid[nx][ny]==-grid[x][y]){
q.push_back({nx,ny});
dist[nx][ny] = dist[x][y]+1;
}
}
}
cout << ans << endl;
}
