#include <bits/stdc++.h>
using namespace std;
const int dx[4] = {-1, 1, 0, 0};
const int dy[4] = {0, 0, -1, 1};
const int INF = 1e9;
int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
int h, w;
cin >> h >> w;
vector<string> adj(h);
for (int i = 0; i < h; i++) cin >> adj[i];
int n = h * w;
vector<int> dis(n, INF);
dis[0] = 0;
deque<int> dq;
dq.emplace_front(0);
while (!dq.empty()){
int id = dq.front();
dq.pop_front();
int d = dis[id];
int x = id / w, y = id % w;
for (int k = 0; k < 4; k++){
int nx = x + dx[k], ny = y + dy[k];
if (nx < 0 || nx >= h || ny < 0 || ny >= w || adj[nx][ny] == '.') continue;
int nid = nx * w + ny;
int wnw = adj[nx][ny] != adj[x][y];
if (dis[nid] > d + wnw){
dis[nid] = d + wnw;
if (wnw == 0)
dq.emplace_front(nid);
else
dq.emplace_back(nid);
}
}
}
int mx = 1;
for (int i = 0; i < h; i++)
for (int j = 0; j < w; j++)
if (adj[i][j] != '.') mx = max(mx, dis[i * w + j]+1);
cout << mx;
}
