#include<bits/stdc++.h>
using namespace std ;
#define maxn 4009
#define ll long long
#define fi first
#define se second
#define pb push_back
#define left id<<1
#define right id<<1|1
#define re exit(0);
#define _lower(v,x) lower_bound(v.begin(),v.end(),x)-v.begin()+1
const int mod = 1e9+7 ;
const int INF = 1e9 ;
const int LOG = 18 ;
typedef vector<int> vi ;
typedef pair<int,int> pii ;
typedef vector<pii> vii ;
typedef vector<ll> vl ;
typedef pair<ll,ll> pll ;
typedef vector<pll> vll ;
void add ( int&a , int b ) { if ((a+=b) > mod ) a -= mod ; }
void sub ( int&a , int b ) { if ((a-=b) < 0 ) a += mod ; }
template<typename T> void chkmin(T& x, T y) {if(x > y) x = y;}
template<typename T> void chkmax(T& x, T y) {if(x < y) x = y;}
void rf ( )
{
freopen ("bai1.inp","r",stdin) ;
// freopen ("bai1.out","w",stdout) ;
}
int _pow ( int a , int n )
{
if ( n == 0 ) return 1 ;
int res = _pow ( a , n / 2 ) ;
if ( n % 2 ) return ( 1ll * res * res % mod * a % mod ) ;
else return ( 1ll * res * res % mod ) ;
}
int n , m ;
char a [maxn][maxn] ;
int dx [] = {0,0,-1,1} ;
int dy [] = {1,-1,0,0} ;
bool inside ( int x , int y )
{
return (x>=1&&x<=n&&y>=1&&y<=m&&a[x][y]!='.') ;
}
int d [maxn][maxn] ;
int main ( )
{
ios_base :: sync_with_stdio (0) ;
cin.tie(0) ; cout.tie(0) ;
// rf () ;
cin >> n >> m ;
for ( int i = 1 ; i <= n ; i ++ ) for ( int j = 1 ; j <= m ; j ++ ) cin >> a [i][j] ;
deque <pii> q ;
memset ( d , 0x3f , sizeof d ) ;
d [1][1] = 1 ;
q . pb ({1,1}) ;
while (!q.empty())
{
int u = q.front().fi , v = q.front().se ;
q.pop_front() ;
for ( int i = 0 ; i < 4 ; i ++ )
{
int x = u + dx [i] , y = v + dy [i] ;
if ( inside (x,y) )
{
if ( a [x][y] == a [u][v] && d[x][y]>d[u][v] ) q.push_front({x,y}) , d [x][y] = d [u][v] ;
else if ( d [x][y] > d [u][v] + 1 )
{
q . pb ({x,y}) ;
d [x][y] = d [u][v] + 1 ;
}
}
}
}
int res = 0 ;
for ( int i = 1 ; i <= n ; i ++ ) for ( int j = 1 ; j <= m ; j ++ )
{
if ( a[i][j] == '.' ) continue ;
chkmax (res,d[i][j]) ;
}
cout << res ;
}
//-std=c++11
