#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define MASK(i) (1ULL << (i))
#define GETBIT(mask, i) (((mask) >> (i)) & 1)
#define ALL(v) (v).begin(), (v).end()
ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll LASTBIT(ll mask){return (mask) & (-mask);}
int pop_cnt(ll mask){return __builtin_popcountll(mask);}
int ctz(ull mask){return __builtin_ctzll(mask);}
int logOf(ull mask){return 63 - __builtin_clzll(mask);}
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rngesus(ll l, ll r){return l + (ull) rng() % (r - l + 1);}
template <class T1, class T2>
bool maximize(T1 &a, T2 b){
if (a < b) {a = b; return true;}
return false;
}
template <class T1, class T2>
bool minimize(T1 &a, T2 b){
if (a > b) {a = b; return true;}
return false;
}
template <class T>
void printArr(T& container, string separator = " ", string finish = "\n", ostream &out = cout){
for(auto item: container) out << item << separator;
out << finish;
}
template <class T>
void remove_dup(vector<T> &a){
sort(ALL(a));
a.resize(unique(ALL(a)) - a.begin());
}
const int N = 4009;
int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};
int n, m;
int grid[N][N];
int dis[N][N];
int main(void){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> m;
vector<string> a(n);
for(int i = 0; i<n; ++i) cin >> a[i];
for(int i = 0; i<n; ++i) for(int j = 0; j<m; ++j) if (a[i][j] == 'R') grid[i+1][j+1] = 1;
else if (a[i][j] == 'F') grid[i+1][j+1] = 2;
memset(dis, 63, sizeof dis);
deque<pair<int, int>> q; q.push_back({1, 1});
dis[1][1] = 1;
int ans = 1;
while(q.size()){
pair<int, int> u = q.front(); q.pop_front();
maximize(ans, dis[u.first][u.second]);
for(int dir = 0; dir < 4; ++dir){
pair<int, int> v = {u.first + dx[dir], u.second + dy[dir]};
if (grid[v.first][v.second] == 0) continue;
if (grid[v.first][v.second] != grid[u.first][u.second]){
if (minimize(dis[v.first][v.second], dis[u.first][u.second] + 1)){
q.push_back(v);
}
}
else{
if (minimize(dis[v.first][v.second], dis[u.first][u.second])){
q.push_front(v);
}
}
}
}
cout << ans << "\n";
return 0;
}
