#include <bits/stdc++.h>
using namespace std;
#define MAXN 4001
int h,w;
int a[MAXN][MAXN];
int dist[MAXN][MAXN];
deque<pair<int,int>> bfsq;
pair<int,int> dir[4];
int ans=0;
bool check(int nodex,int nodey)
{
if (nodex>=1 and nodex<=h and nodey>=1 and nodey<=w and a[nodex][nodey]!='.' and dist[nodex][nodey]==INT_MAX) return true;
return false;
}
void bfs()
{
for (int i=1;i<=h;i++)
{
for (int j=1;j<=w;j++) dist[i][j]=INT_MAX;
}
dist[1][1]=0;bfsq.push_front({1,1});
while (bfsq.empty()==false)
{
int nodex=bfsq.front().first,nodey=bfsq.front().second;bfsq.pop_front();
ans=max(ans,dist[nodex][nodey]);
for (int i=0;i<4;i++)
{
int sledx=nodex+dir[i].first,sledy=nodey+dir[i].second;
if (!check(sledx,sledy)) continue;
if (a[sledx][sledy]==a[nodex][nodey]) {dist[sledx][sledy]=dist[nodex][nodey];bfsq.push_front({sledx,sledy});}
else {dist[sledx][sledy]=dist[nodex][nodey]+1;bfsq.push_back({sledx,sledy});}
}
}
}
int main()
{
dir[0]={0,1},dir[1]={1,0},dir[2]={0,-1},dir[3]={-1,0};
cin>>h>>w;
for (int i=1;i<=h;i++)
{
string s;cin>>s;
for (int j=1;j<=w;j++) a[i][j]=s[j-1];
}
bfs();
cout<<ans+1<<endl;
}
