// Deep Prajapati
#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef long double ldb;
#define nl "\n"
#define yes "YES\n"
#define no "NO\n"
#define vin vector<int>
#define vll vector<ll>
#define pii pair<int, int>
#define pll pair<ll, ll>
const int mod = 1000000007;
void pwp(ldb x, int p) { cout<<fixed<<setprecision(p)<<x<<nl; }
// priority_queue<pq_dt,vector<pq_dt>,decltype(comp)> pq(comp);
queue<pair<pii, int>> q;
bool is_valid(int i, int j, int h, int w) {return (i < h && i >= 0 && j<w && j>=0);}
void visit(pii src, int num, vector<string> &adj){
int h = adj.size();
int w = adj[0].size();
queue<pii> q1;
q1.push(src);
char curr = adj[src.first][src.second];
adj[src.first][src.second] = 'V';
vector<pii> dir = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
while(!q1.empty()){
pii s = q1.front();
q1.pop();
for(pii d : dir){
int i = s.first + d.first;
int j = s.second + d.second;
if(!is_valid(i, j, h, w)) continue;
if(adj[i][j] != curr){
if(adj[i][j] != 'V' && adj[i][j] != '.'){
q.push(make_pair(make_pair(i, j), num+1));
}
continue;
}
adj[i][j] = 'V';
q1.push(make_pair(i, j));
}
}
}
void run_case() {
int h, w;
cin>>h>>w;
vector<string> adj(h);
for(int i = 0;i<h;i++) cin>>adj[i];
int ans = 0;
q.push(make_pair(make_pair(0, 0), 1));
while(!q.empty()){
pii s = q.front().first;
if(adj[s.first][s.second] == 'V'){
q.pop();
continue;
}
ans = max(ans, q.front().second);
visit(s, q.front().second, adj);
q.pop();
}
cout<<ans<<nl;
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
ll t = 1;
// cin >> t;
while (t--) run_case();
return 0;
}
// ---------- lemonade have lemons in it ---------- //
