#include <bits/stdc++.h>
#define f first
#define s second
using namespace std;
const int MAXN = 4010;
char grid[MAXN][MAXN];
int dist[MAXN][MAXN];
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int H,W; cin >> H >> W;
for(int i = 1;i<=H;++i){
for(int j = 1;j<=W;++j){
cin >> grid[i][j];
}
}
int ans = 0;
int dx[4] = {0,0,1,-1}, dy[4] = {1,-1,0,0};
dist[1][1] = 1;
deque<pair<int,int>> q; q.push_back({1,1});
while(!q.empty()){
int r = q.front().f, c = q.front().s; q.pop_front();
ans = max(ans,dist[r][c]);
//cout << r << " " << c << " " << dist[r][c] << "\n";
for(int i = 0;i<4;++i){
int nr = r+dx[i], nc = c+dy[i];
if(nr < 1 || nc < 1 || nr > H || nc > W) continue;
if(dist[nr][nc] == 0){
if(grid[nr][nc] == '.') continue;
if(grid[r][c] != grid[nr][nc]){
q.push_back({nr,nc});
dist[nr][nc] = dist[r][c]+1;
}
else{
q.push_front({nr,nc});
dist[nr][nc] = dist[r][c];
}
}
}
}
cout << ans << "\n";
return 0;
}
