#include <iostream>
#include <deque>
using namespace std;
const int N=4001;
char mat[N][N];
bool viz[N][N];
int n,m;
int ans=0;
struct coada
{
int x,y,val;
};
int dx[]={1,0,-1,0};
int dy[]={0,-1,0,1};
bool inmat(int i,int j)
{
return(i<=n&&i>=1&&j<=m&&j>=1);
}
deque<coada>dq;
void citeste()
{
cin>>n>>m;
for(int i=1;i<=n;i++)
{
for(int j=1;j<=m;j++)
cin>>mat[i][j];
}
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int test;
citeste();
dq.push_front({1,1,1});
while(!dq.empty())
{
int x=dq.front().x;
int y=dq.front().y;
int val=dq.front().val;
dq.pop_front();
if(viz[x][y])
continue;
viz[x][y]=true;
ans=max(val,ans);
for(int i=0;i<4;i++)
{
int a=x+dx[i];
int b=y+dy[i];
if(!inmat(a,b))
continue;
if(mat[a][b]=='.')
continue;
if(viz[a][b])
continue;
if(mat[a][b]!=mat[x][y])
dq.push_back({a,b,val+1});
else
dq.push_front({a,b,val});
}
}
cout<<ans;
return 0;
}
