#include <bits/stdc++.h>
#define fastio cin.tie(0)->ios::sync_with_stdio(0);
using namespace std;
const int NMAX = 4e3;
const int dx[] = {0,0,1,-1}, dy[] = {1,-1,0,0};
typedef pair<int,int> pii;
int H,W, dist[NMAX + 10][NMAX + 10];
char meadow[NMAX + 10][NMAX + 10];
void solve(){
deque<pii> q;
q.push_back({0,0}); dist[0][0] = 0;
while(!q.empty()){
int x = q.back().first, y = q.back().second;
q.pop_back();
for(int i=0;i<4;i++){
int nx = x + dx[i];
int ny = y + dy[i];
if(nx < 0 || ny < 0 || nx >= H || ny >= W) continue;
if(meadow[nx][ny] == '.') continue;
int w = (meadow[x][y] == meadow[nx][ny]) ? 0 : 1;
if(dist[nx][ny] <= dist[x][y] + w) continue;
dist[nx][ny] = dist[x][y] + w;
if(w == 0) q.push_back({nx,ny});
else q.push_front({nx,ny});
}
}
int ans = 0;
for(int i=0;i<H;i++){
for(int j=0;j<W;j++){
if(meadow[i][j] == '.') continue;
ans = max(ans, dist[i][j] + 1);
}
}
cout << ans;
}
int main(){
fastio;
cin >> H >> W;
for(int i=0;i<H;i++){
string s; cin >> s;
for(int j=0;j<W;j++){
meadow[i][j] = s[j];
dist[i][j] = 1e9;
}
}
solve();
}
