#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> pii;
const int MN=4e3+2;
int H,W,ans=0;
char gr[MN][MN];
bool vis[MN][MN];
bool chk(int r,int c) {
return r>0&&c>0&&r<=H&&c<=W&&gr[r][c]!='.'&&!vis[r][c];
}
int main() {
ios::sync_with_stdio(0);cin.tie(0);
cin>>H>>W;
for(int i=1;i<=H;++i) cin>>(gr[i]+1);
queue<pii> q,nq;
q.push({1,1});
vis[1][1]=1;
while(1) {
++ans;
while(!q.empty()) {
int r=q.front().first,c=q.front().second;
q.pop();
if(chk(r+1,c)) {
vis[r+1][c]=1;
if(gr[r][c]==gr[r+1][c]) q.push({r+1,c});
else nq.push({r+1,c});
}
if(chk(r-1,c)) {
vis[r-1][c]=1;
if(gr[r][c]==gr[r-1][c]) q.push({r-1,c});
else nq.push({r-1,c});
}
if(chk(r,c+1)) {
vis[r][c+1]=1;
if(gr[r][c]==gr[r][c+1]) q.push({r,c+1});
else nq.push({r,c+1});
}
if(chk(r,c-1)) {
vis[r][c-1]=1;
if(gr[r][c]==gr[r][c-1]) q.push({r,c-1});
else nq.push({r,c-1});
}
}
swap(nq,q);
if(q.empty()) break;
}
cout<<ans<<'\n';
return 0;
}
