#include <iostream>
#include <queue>
#include <vector>
#include <algorithm>
#include <set>
using namespace std;
const int MAX_H=4000,MAX_W=4000;
bool visited[MAX_H][MAX_W];
char grid[MAX_H][MAX_W];
int dist[MAX_H][MAX_W];
//L,R,U,D
vector<int> dx={0,0,-1,1};
vector<int> dy={-1,1,0,0};
int main() {
int h,w; cin >> h >> w;
for(int i=0; i<h; i++) {
for(int j=0; j<w; j++) {
cin >> grid[i][j];
}
}
deque<pair<int,int>> q;
q.push_back(make_pair(0,0));
while(!q.empty()) {
pair<int,int> v=q.front();
q.pop_front();
for(int i=0; i<4; i++) {
pair<int,int> u={v.first+dx[i],v.second+dy[i]};
if(u.first<0 || u.first>=h || u.second<0 || u.second>=w || visited[u.first][u.second] || grid[u.first][u.second]=='.') continue;
if(grid[v.first][v.second]==grid[u.first][u.second]) {
dist[u.first][u.second]=dist[v.first][v.second];
q.push_front(make_pair(u.first,u.second));
}
else {
dist[u.first][u.second]=dist[v.first][v.second]+1;
q.push_back(make_pair(u.first,u.second));
}
}
}
int ans=0;
for(int i=0; i<h; i++) {
for(int j=0; j<w; j++) {
if(visited[i][j]) ans=max(ans,dist[i][j]);
}
}
cout << ans;
return 0;
}
