#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define fi first
#define se second
#define pii pair<int, int>
#define pb push_back
#define vi vector<int>
#define all(x) x.begin(), x.end()
using namespace std;
using namespace __gnu_pbds;
using ll = long long int;
using ull = unsigned long long int;
constexpr ll mod = 1e9 + 7;
constexpr ll INF = LONG_LONG_MAX;
int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};
int main()
{
//tree<ll, null_type,less<ll>, rb_tree_tag,tree_order_statistics_node_update> q;
/*freopen("problemname.in", "r", stdin);
freopen("problemname.out", "w", stdout);*/
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int n, m;
cin >> n >> m;
char a[n][m];
for(int i = 0;i<n;++i) {
for(int j = 0;j<m;++j) {
cin >> a[i][j];
}
}
int c = -1;
int cmp[n][m];
memset(cmp, -1, sizeof cmp);
bool vis[n][m];
memset(vis, false, sizeof vis);
for(int i = 0;i<n;++i) {
for(int j = 0;j<m;++j) {
if (!vis[i][j] && (a[i][j] == 'F' || a[i][j] == 'R')) {
queue<pii> q;
q.push({i, j});
vis[i][j] = true;
cmp[i][j] = ++c;
while(!q.empty()) {
pii node = q.front();
q.pop();
for(int k = 0;k<4;++k) {
int x = node.fi + dx[k], y = node.se + dy[k];
if (x >= 0 && y >= 0 && x < n && y < m) {
if (!vis[x][y] && a[x][y] == a[i][j]) {
vis[x][y] = true;
cmp[x][y] = c;
q.push({x, y});
}
}
}
}
}
}
}
set<int> adj[c + 1];
memset(vis, false, sizeof vis);
for(int i = 0;i<n;++i) {
for(int j = 0;j<m;++j) {
if (!vis[i][j] && (a[i][j] == 'F' || a[i][j] == 'R')) {
queue<pii> q;
q.push({i, j});
vis[i][j] = true;
while(!q.empty()) {
pii node = q.front();
q.pop();
for(int k = 0;k<4;++k) {
int x = node.fi + dx[k], y = node.se + dy[k];
if (x >= 0 && y >= 0 && x < n && y < m) {
if (!vis[x][y] && a[x][y] == a[i][j]) {
vis[x][y] = true;
q.push({x, y});
}
if (a[x][y] != a[i][j] && a[x][y] != '.') {
adj[cmp[i][j]].insert(cmp[x][y]);
}
}
}
}
}
}
}
int d[c + 1];
d[0] = 0;
queue<int> q;
q.push(0);
bool vv[c + 1];
memset(vv, false, sizeof vv);
vv[0] = true;
while(!q.empty()) {
int node = q.front();
q.pop();
for(const int& v:adj[node]) {
if (!vv[v]) {
vv[v] = true;
d[v] = d[node] + 1;
q.push(v);
}
}
}
cout << *max_element(d, d + c + 1) + 1 << endl;
return 0;
}
