#include <bits/stdc++.h>
using namespace std;
vector <vector <char>> mat;
int bfs (int n, int m, vector <vector <int>> &g)
{
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();
for (auto i: g[prvi])
{
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);
int n, m;
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];
}
}
vector <vector <int>> g(n*m);
for (int i=0; i<n; i++)
{
for (int j=0; j<m; j++)
{
if (mat[i][j]=='.')
{
continue;
}
if (j!=0 && mat[i][j-1]!='.') g[m*i+j].push_back(m*i+j-1);
if (j!=m-1 && mat[i][j+1]!='.') g[m*i+j].push_back(m*i+j+1);
if (i!=0 && mat[i-1][j]!='.') g[m*i+j].push_back(m*(i-1)+j);
if (i!=n-1 && mat[i+1][j]!='.') g[m*i+j].push_back(m*(i+1)+j);
}
}
cout<<bfs(n, m, g)<<endl;
return 0;
}
