#include<bits/stdc++.h>
using namespace std;
typedef pair<int, int> pii;
#define f first
#define s second
const int MAX_W = 4005;
int N, M;
char L[MAX_W][MAX_W];
int dep[MAX_W][MAX_W];
bool vis[MAX_W][MAX_W];
pii Move[4] = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
int main ()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> N >> M;
for (int i = 0; i <= N + 1; i++)
{
for (int j = 0; j < M + 1; j++)
{
if (i == 0 || j == 0 || i == N + 1 || j == M + 1)
{
L[i][j] = '.';
continue;
}
cin >> L[i][j];
}
}
/*for (int i = 0; i <= N + 1; i++)
{
for (int j = 0; j < M + 1; j++)
{
cout << L[i][j];
}
cout << '\n';
}*/
//cout << '\n';
deque<pii> q;
q.push_front({1, 1});
int ans = 1;
dep[1][1] = 1;
vis[1][1] = true;
while (!q.empty())
{
//cout << "size = " << q.size() << '\n';
pii pos = q.front();
//cout << "pos = {" << pos.f << ", " << pos.s << "}\n";
//cout << "val: " << L[pos.f][pos.s] << '\n';
q.pop_front();
pii newpos;
for (int i = 0; i < 4; i++)
{
newpos = {pos.f + Move[i].f, pos.s + Move[i].s};
if (vis[newpos.f][newpos.s] || (L[newpos.f][newpos.s] != 'F' && L[newpos.f][newpos.s] != 'R')) continue;
vis[newpos.f][newpos.s] = true;
if (L[newpos.f][newpos.s] == L[pos.f][pos.s])
{
dep[newpos.f][newpos.s] = dep[pos.f][pos.s];
q.push_front(newpos);
}
else
{
dep[newpos.f][newpos.s] = dep[pos.f][pos.s] + 1;
ans = max(ans, dep[pos.f][pos.s] + 1);
q.push_back(newpos);
}
}
}
cout << ans;
}
