#include <bits/stdc++.h>
using namespace std;
int n, m;
vector <vector <char>> mat;
vector <int> sus (int prvi)
{
int i=prvi/m, j=prvi%m;
vector <int> ans;
if (mat[i][j]=='.') return {};
if (j!=0 && mat[i][j-1]!='.') ans.push_back(m*i+j-1);
if (j!=m-1 && mat[i][j+1]!='.') ans.push_back(m*i+j+1);
if (i!=0 && mat[i-1][j]!='.') ans.push_back(m*(i-1)+j);
if (i!=n-1 && mat[i+1][j]!='.') ans.push_back(m*(i+1)+j);
return ans;
}
int bfs ()
{
deque <int> kju;
vector <int> mindist(n*m, 1e7);
kju.push_front(0);
mindist[0]=0;
while (!kju.empty())
{
int prvi=kju.front();
kju.pop_front();
vector <int> susedi=sus(prvi);
for (auto i: susedi)
{
int dist=(mat[prvi/m][prvi%m]!=mat[i/m][i%m]);
if (mindist[i]>mindist[prvi]+dist)
{
mindist[i]=mindist[prvi]+dist;
if (!dist)
{
kju.push_front(i);
}
else
{
kju.push_back(i);
}
}
}
}
int maxdist=0;
for (auto i: mindist)
{
if (i!=1e7) maxdist=max(maxdist, i);
}
return 1+maxdist;
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin>>n>>m;
mat.resize(n, vector <char> (m));
for (int i=0; i<n; i++)
{
for (int j=0; j<m; j++)
{
cin>>mat[i][j];
}
}
cout<<bfs()<<endl;
return 0;
}
