#include <bits/stdc++.h>
// #define int long long
#define vi vector<int>
#define ii pair<int, int>
#define f first
#define s second
#define all(x) (x).begin(), (x).end()
#define P 31
#define mod 1'000'000'007
#define inf 1'000'000'000'000
#define pb push_back
#define str string
#define sz(x) (x).size()
#define vvi vector<vi>
#define fun function
#define oopt cin.tie(0);cout.tie(0);ios_base::sync_with_stdio(false);
#define file freopen("problemname.in", "r", stdin); freopen("pr.out", "w", stdout);
#define dbg(v) cout << "Line(" << __LINE__ << ") -> " << #v << " = " << (v) << endl;
using namespace std;
template <class T, int SZ> using arr = array<T, SZ>;
int a[4001][4001];
int comp[4001][4001];
vi graf[20000001];
set<ii> pov;
vector<ii> pr = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
void dfs(int i, int j, int nc, int n, int m)
{
if (comp[i][j]) return;
comp[i][j] = nc;
for (ii d : pr)
{
int ni = i+d.f, nj = j+d.s;
if (ni < 0 || nj < 0 || nj >= m || ni >= n) continue;
dfs(ni, nj, nc, n, m);
}
}
int dfs1(int u, int p = -1)
{
int rez = 0;
for (int v : graf[u])
if (v != p)
rez = max(rez, dfs1(v, u));
return rez+1;
}
signed main()
{
oopt;
int n, m;
cin >> n >> m;
for (int i = 0; i < n; i++)
for (int j = 0; j < m; j++)
{
char c;
cin >> c;
if (c == 'F') a[i][j] = 1;
else if (c == 'R') a[i][j] = 2;
}
int nc = 1;
for (int i = 0; i < n; i++)
for (int j = 0; j < m; j++)
dfs(i, j, nc++, n, m);
for (int i = 0; i < n; i++)
for (int j = 0; j < m; j++)
{
for (ii d : pr)
{
int ni = i+d.f, nj = j+d.s;
if (ni < 0 || nj < 0 || nj >= m || ni >= n) continue;
if (pov.find({comp[ni][nj], comp[i][j]}) != pov.end()) continue;
pov.insert({comp[ni][nj], comp[i][j]});
pov.insert({comp[ni][nj], comp[i][j]});
graf[comp[nj][ni]].pb(comp[i][j]);
graf[comp[i][j]].pb(comp[nj][ni]);
}
}
cout << dfs1(comp[0][0]) << "\n";
return 0;
}
