#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 p[16000005];
int a[4001][4001];
bool ob[16000005];
set<int> pov[16000005];
int par(int x) {return p[x] = (p[x] == x ? x : par(p[x]));};
void zd(int x, int y)
{
x = par(x);
y = par(y);
if (x == y) return;
if (pov[x].size() < pov[y].size())
swap(x, y);
for (int v : pov[y])
pov[x].insert(v);
pov[y].clear();
p[y] = x;
}
int dfs(int u, int p = -1)
{
// cout << u << " <- " << p << "\n";
int rez = 0;
for (int v : pov[u])
if (v != p)
rez = max(rez, dfs(v, u));
return rez+1;
}
vector<ii> pr = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
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;
p[i*m+j] = i*m+j;
}
queue<ii> q;
q.push({0, 0});
while (q.size())
{
ii t = q.front();
q.pop();
int i = t.f, j = t.s;
int x = i*m+j, y = 0;
for (ii d : pr)
{
int ni = i+d.f, nj = j+d.s;
y = ni*m+nj;
if (ni < 0 || nj < 0 || ni > n || nj > m || ob[par(y)] || a[ni][nj] == 0) continue;
if (a[ni][nj] != a[i][j]) continue;
zd(x, y);
ob[par(y)] = 1;
q.push({ni, nj});
}
for (ii d : pr)
{
int ni = i+d.f, nj = j+d.s;
y = ni*m+nj;
if (ni < 0 || nj < 0 || ni > n || nj > m || ob[par(y)] || a[ni][nj] == 0) continue;
ob[par(y)] = 1;
// cout << par(x) << " " << par(y) << "t\n";
pov[par(x)].insert(par(y));
pov[par(y)].insert(par(x));
q.push({ni, nj});
}
}
cout << dfs(0) << "\n";
return 0;
}
