#include<bits/stdc++.h>
#define fi first
#define se second
#define int long long
using namespace std;
using db=double;
using ll=int64_t;
using sll=__int128;
using lb=long double;
int32_t main(){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0); srand(time(0));
int h,w; cin>>h>>w; vector<vector<char>>a(h+1,vector<char>(w+1)); int dx[]={0,0,1,-1}; int dy[]={1,-1,0,0};
for(int i=1; i<=h; i++){
for(int j=1; j<=w; j++){
cin>>a[i][j];
}
}
auto check=[&](int x, int y){
if(x<1 || y<1 || x>h || y>w || a[x][y]=='.')return false;
return true;
};
deque<pair<int,int>>dq; vector<vector<int>>dist(h+1,vector<int>(w+1,-1)); dq.push_back({1,1}); dist[1][1]=1; int ans=0;
while(dq.size()){
int x=dq.front().fi; int y=dq.front().se; dq.pop_front(); ans=max(ans,dist[x][y]);
for(int i=0; i<4; i++){
int nx=x+dx[i]; int ny=y+dy[i];
if(check(nx,ny) && dist[nx][ny]==-1){
if(a[x][y]==a[nx][ny]){
dist[nx][ny]=dist[x][y]; dq.push_front({nx,ny});
}else{
dist[nx][ny]=dist[x][y]+1; dq.push_back({nx,ny});
}
}
}
}
cout<<ans<<'\n';
}
/*
O what can ail thee, knight-at-arms,
Alone and palely loitering?
The sedge has withered from the lake,
And no birds sing.
O what can ail thee, knight-at-arms,
So haggard and so woe-begone?
The squirrel’s granary is full,
And the harvest’s done.
I see a lily on thy brow,
With anguish moist and fever-dew,
And on thy cheeks a fading rose
Fast withereth too.
*/
