#include <bits/stdc++.h>
using namespace std;
#define int long long
int dx[4]={1,-1,0,0},dy[4]={0,0,1,-1};
vector<string> snow(4000);
vector<vector<int>> depth(4000,vector<int>(4000));
int n,m,ans=1;
bool inside(int x, int y)
{
if(-1<x&&x<n&&-1<y&&y<m&&snow[x][y]!='.')
{
return true;
}
return false;
}
signed main() {
iostream::sync_with_stdio(false);
cin.tie(0);cout.tie(0);
cin >> n >> m;
for(int i=0;i<n;i++)
{
cin >> snow[i];
}
depth[0][0]=1;
deque<pair<int,int>> q;
q.push_back({0,0});
while(q.size())
{
pair<int,int> now = q.front();
q.pop_front();
ans = max(ans,depth[now.first][now.second]);
for(int i=0;i<4;i++)
{
int x=now.first + dx[i],y=now.second + dy[i];
if(inside(x,y)&&depth[x][y]==0)
{
if(snow[x][y]==snow[now.first][now.second])
{
depth[x][y]=depth[now.first][now.second];
q.push_front({x,y});
}
else
{
depth[x][y]=depth[now.first][now.second]+1;
q.push_back({x,y});
}
}
}
}
cout<<ans;
}
