#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pr pair<int, int>
#define f first
#define s second
#define pb push_back
const int ndim=4001;
int ns;
string mps[ndim];
vector<vector<int>> level(ndim, vector<int> (ndim, -1));
int h, w;
int dx[4]={1, -1, 0, 0};
int dy[4]={0, 0, 1, -1};
bool check(int x, int y){
if(x>=0 && x<h && y>=0 && y<w && mps[x][y]!='.') return true;
else return false;
}
int main(){
cin>>h>>w;
for (int i=0; i<h; i++) cin>>mps[i];
deque<pr> q;
q.push_front({0, 0}); // x, y
level[0][0]=1;
int ans=0;
while(!q.empty()){
pr nd=q.front(); q.pop_front();
ans=max(ans, level[nd.f][nd.s]);
for (int i=0; i<4; i++){
int x=nd.f+dx[i]; int y=nd.s+dy[i];
if(check(x, y) && level[x][y]==-1){
if(mps[x][y]==mps[nd.f][nd.s]){
q.push_front({x, y});
level[x][y]=level[nd.f][nd.s];
}
else{
q.push_back({x, y});
level[x][y]=level[nd.f][nd.s]+1;
}
}
}
}
cout<<ans<<endl;
}
