#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
const int maxn = 4010;
int dx[4] = {0,0,1,-1}, dy[4] = {1,-1,0,0};
ll h, w, prof[maxn][maxn], resp = 1;
string neve[maxn];
bool dentro(ll novox, ll novoy){
if(novox < 0) return false;
if(novox >= h) return false;
if(novoy < 0) return false;
if(novoy >= w) return false;
if(neve[novox][novoy] == '.') return false;
return true;
}
int main(){
cin >> h >> w;
for(int i = 0; i < h; i++) cin >> neve[i];
deque<pair<ll,ll>>q;
q.push_back({0,0});
prof[0][0] = 1;
while(!q.empty()){
ll atx = q.front().first, aty = q.front().second;
q.pop_front();
resp = max(resp,prof[atx][aty]);
for(int i = 0; i < 4; i++){
ll novox = atx+dx[i], novoy = aty+dy[i];
if(dentro(novox,novoy) && !prof[novox][novoy]){
if(neve[novox][novoy] == neve[atx][aty]){
prof[novox][novoy] = prof[atx][aty];
q.push_front({novox,novoy});
}
else{
prof[novox][novoy] = prof[atx][aty]+1;
q.push_back({novox,novoy});
}
}
}
}
cout << resp << "\n";
return 0;
}
