#include <bits/stdc++.h>
using namespace std;
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int a[4000][4000];
bool visited[4000][4000]{false};
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
int h, w;
cin >> h >> w;
char ch;
for (int i = 0; i < h; i++)
{
for (int j = 0; j < w; j++)
{
cin >> ch;
if (ch == 'F')
a[i][j] = 1;
else if (ch == 'R')
a[i][j] = 2;
else
a[i][j] = 3;
}
}
int ans = 1;
set<vector<int>> q;
vector<int> s;
int ii, jj;
q.insert({1, 0, 0});
visited[0][0] = true;
while (!q.empty())
{
s = *q.begin();
q.erase(q.begin());
for (int i = 0; i < 4; i++)
{
ii = s[1] + dx[i];
jj = s[2] + dy[i];
if (ii >= 0 && ii < h && jj >= 0 && jj < w && !visited[ii][jj] && a[ii][jj] != 3)
{
visited[ii][jj] = true;
if (a[ii][jj] == a[s[1]][s[2]])
{
q.insert({s[0], ii, jj});
}
else
{
ans = max(ans, s[0] + 1);
q.insert({s[0] + 1, ii, jj});
}
}
}
}
cout << ans << "\n";
}
