#include <bits/stdc++.h>
using namespace std;
int dx[4] = {0,1,-1,0};
int dy[4] = {1,0,0,-1};
int dist[4000][4000];
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0);
int H,W; cin >> H >> W;
vector<string> grid(H);
for(int i = 0;i<H;++i) cin >> grid[i];
deque<pair<int,int>> q; q.push_front({0,0});
dist[0][0] = 1;
int ans = 1;
while(!q.empty()){
int x = q.front().first, y = q.front().second; q.pop_front();
ans = max(ans,dist[x][y]);
for(int i = 0;i<4;++i){
int nx = x+dx[i], ny = y+dy[i];
if(nx < 0 || nx >= H || ny < 0 || ny >= W) continue;
if(grid[nx][ny] == '.' || dist[nx][ny] != 0) continue;
if(grid[nx][ny] == grid[x][y]){
dist[nx][ny] = dist[x][y];
q.push_front({nx,ny});
}
else{
dist[nx][ny] = dist[x][y]+1;
q.push_back({nx,ny});
}
}
}
cout << ans << "\n";
return 0;
}
