#include <bits/stdc++.h>
using namespace std;
using tii = tuple<int,int,int>;
const int N = 4005;
char a[N][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++ )
{
for( int j=0;j<w;j++ )
{
cin >> a[i][j];
}
}
int ans = 0;
priority_queue<tii, vector<tii>, greater<tii>> pq;
pq.push( {1, 0, 0} );
dp[0][0] = 1;
while( !pq.empty() )
{
auto [_, r, c] = pq.top();
pq.pop();
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];
else dp[nr][nc] = dp[r][c]+1;
pq.push( {dp[nr][nc], nr, nc} );
}
}
cout << ans << "\n";
}
