#include <bits/stdc++.h>
using namespace std;
using pii = pair<int,int>;
const int N = 4005;
string a[N];
int h, w, dp[N][N];
int diry[] = {0, 1, 0, -1}, dirx[] = {1, 0, -1, 0};
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0);
cin >> h >> w;
for( int i=0;i<h;i++ )
{
cin >> a[i];
}
int ans = 0;
deque<pii> q;
q.push_back( {0, 0} );
dp[0][0] = 1;
while( !q.empty() )
{
auto [r, c] = q.front();
q.pop_front();
ans = max( ans, dp[r][c] );
for( int i=0;i<4;i++ )
{
int nr = r+diry[i], nc = c+dirx[i];
if( nr>=h || nc>=w || nr<0 || nc<0 || a[nr][nc] == '.' ) continue;
if( dp[nr][nc] ) continue;
if( a[r][c] == a[nr][nc] )
{
dp[nr][nc] = dp[r][c];
q.push_front( {nr, nc} );
}
else
{
dp[nr][nc] = dp[r][c]+1;
q.push_back( {nr, nc} );
}
}
}
cout << ans << "\n";
}
