#include<bits/stdc++.h>
using namespace std;
#define int long long
int X[]={-1,1,0,0};
int Y[]={0,0,-1,1};
int used[4001][4001],dist[4001][4001];
signed main()
{
int n,m,emix=0;
cin>>n>>m;
char a[n+1][m+1];
for(int i=1;i<=n;i++){for(int j=1;j<=m;j++){cin>>a[i][j];};};
deque <pair <int,int> > dq;
dq.push_back({1,1});
used[1][1]=1;
while(!dq.empty())
{
int x=dq.front().first;
int y=dq.front().second;
dq.pop_front();
for(int i=0;i<4;i++)
{
int to_x=X[i]+x;
int to_y=Y[i]+y;
if(!to_x || !to_y || to_x>n || to_y>m || used[to_x][to_y] || !(a[x][y]-'.'))continue;
if(a[to_x][to_y]-a[x][y])
{
dq.push_back({to_x,to_y});
used[to_x][to_y]=1;
dist[to_x][to_y]=dist[x][y]+1;
emix=max(emix,dist[x][y]+1);
}else
{
dq.push_front({to_x,to_y});
used[to_x][to_y]=1;
dist[to_x][to_y]=dist[x][y];
emix=max(emix,dist[x][y]);
}
}
}
cout<<emix;
}
//MBOI Mirbek Bakirov's Olympiad in Informatics :)
