#include <bits/stdc++.h>
using namespace std;
int n,m;
char grid[4001][4001];
int dist[4001][4001];
int di[]={0,0,1,-1};
int dj[]={1,-1,0,0};
int result=0;
bool valid(int i,int j)
{
return 0<=i&&i<n&&0<=j&&j<m&&grid[i][j]!='.'&&dist[i][j]==0;
}
void bfs(int i,int j)
{
deque<pair<int,int>> dq;
dq.push_front({i,j});
dist[i][j]=1;
while(!dq.empty())
{
int ci=dq.front().first;
int cj=dq.front().second;
dq.pop_front();
result=max(result,dist[ci][cj]);
for(int k=0;k<4;k++)
{
int ni=ci+di[k];
int nj=cj+dj[k];
if(valid(ni,nj))
{
if(grid[ci][cj]==grid[ni][nj])
{
dq.push_front({ni,nj});
dist[ni][nj]=dist[ci][cj];
}
else
{
dq.push_back({ni,nj});
dist[ni][nj]=dist[ci][cj]+1;
}
}
}
}
}
int main()
{
cin >> n >> m;
for(int i=0;i<n;i++)
cin >> grid[i];
bfs(0,0);
cout << result;
}
