#include <bits/stdc++.h>
#define endl '\n'
#define ll long long
using namespace std;
const int N = 4005;
int dist[N][N];
string ar[N];
int px[] = {0,0,1,-1};
int py[] = {1,-1,0,0};
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
int n,m;
cin>>n>>m;
for(int i=0;i<n;i++){
cin>>ar[i];
for(int j=0;j<m;j++)dist[i][j]=2e9;
}
deque<pair<int,int>>dq;
dist[0][0]=1;
dq.push_back({0,0});
int ans = 0;
while(!dq.empty()){
auto[x,y]=dq.front();
dq.pop_front();
ans=max(ans,dist[x][y]);
for(int i=0;i<4;i++){
int nx=x+px[i];
int ny=y +py[i];
if(nx<0||nx>=n||ny<0||ny>=m) continue;
if(ar[nx][ny]=='.') continue;
int w=(ar[x][y]==ar[nx][ny]?0:1);
if(dist[x][y] + w < dist[nx][ny]){
dist[nx][ny] = dist[x][y] + w;
if(w==0) dq.push_front({nx,ny});
else dq.push_back({nx,ny});
}
}
}
cout << ans << endl;
}
