#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define int long long
#define ld long double
#define pb push_back
#define pii pair<int, int>
#define all(x) (x).begin(), (x).end()
#define f first
#define s second
void solve() {
ll n, m; cin>>n>>m;
vector<string> s(n);
for(int i=0;i<n;i++) cin>>s[i];
vector<vector<ll>> dist(n, vector<ll>(m, 0));
ll ans=0;
deque<pii> q;
q.push_front({0, 0});
dist[0][0]=1;
ll dx[4]={-1, 1, 0, 0}, dy[4]={0, 0, -1, 1};
while(!q.empty()){
pii i=q.front();q.pop_front();
ans=max(ans, dist[i.f][i.s]);
for(int k=0;k<4;k++){
ll ni=i.f+dx[k];
ll nj=i.s+dy[k];
if(ni>=0 && ni<n && nj>=0 && nj<m && s[ni][nj]!='.' && dist[ni][nj]==0){
if(s[ni][nj]==s[i.f][i.s]){
dist[ni][nj]=dist[i.f][i.s];
q.push_front({ni, nj});
}else{
dist[ni][nj]=dist[i.f][i.s]+1;
q.push_back({ni, nj});
}
}
}
}
cout<<ans;
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
return 0;
}
