#include <bits/stdc++.h>
using namespace std;
#define MAXN 4010
long long n;
long long m;
char matrica[MAXN][MAXN];
long long dist[MAXN][MAXN];
deque<pair<long long,long long>> bfsq;
long long sx[5];
long long sy[5];
long long ans;
bool unutar(long long a,long long b)
{
if (a>=1 and a<=n and b>=1 and b<=m and matrica[a][b]!='.') return true;
else return false;
}
void bfs(long long x,long long y)
{
for (long long i=0;i<MAXN;i++)
{
for (long long j=0;j<MAXN;j++) dist[i][j]=LLONG_MAX;
}
dist[x][y]=0;
bfsq.push_front({x,y});
ans=0;
while (bfsq.empty()==false)
{
long long nodex=bfsq.front().first;
long long nodey=bfsq.front().second;
bfsq.pop_front();
ans=max(ans,dist[nodex][nodey]);
for (long long i=1;i<=4;i++)
{
long long sledx=nodex+sx[i];
long long sledy=nodey+sy[i];
if (unutar(sledx,sledy) and dist[sledx][sledy]==LLONG_MAX)
{
if (matrica[nodex][nodey]==matrica[sledx][sledy])
{
dist[sledx][sledy]=dist[nodex][nodey];
bfsq.push_front({sledx,sledy});
}
else
{
dist[sledx][sledy]=dist[nodex][nodey]+1;
bfsq.push_back({sledx,sledy});
}
}
}
}
}
int main()
{
sx[1]=1,sy[1]=0;
sx[2]=-1,sy[2]=0;
sx[3]=0,sy[3]=1;
sx[4]=0,sy[4]=-1;
cin>>n>>m;
for (long long i=1;i<=n;i++)
{
for (long long j=1;j<=m;j++) cin>>matrica[i][j];
}
bfs(1,0);
cout<<ans<<endl;
}
