#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int mx=4000;
char a[mx][mx];
bool vis[mx][mx];
int dist[mx][mx];
int dx[4] = {0, 1, 0, -1};
int dy[4] = {1, 0, -1, 0};
int n, m;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
memset(vis, 0, sizeof(vis));
memset(dist, 0x3f, sizeof(dist));
cin>>n>>m;
for(int i=0;i<n;i++)for(int j=0;j<m;j++)cin>>a[i][j];
deque<pair<int, int>> q;
q.push_front({0, 0});
dist[0][0]=1;
int mxd=0;
while(!q.empty()){
auto [x, y] = q.front();
q.pop_front();
if(vis[x][y])continue;
vis[x][y]=1;
mxd=max(mxd, dist[x][y]);
for(int i=0;i<4;i++){
int nx = x+dx[i], ny=y+dy[i];
if(nx<0||ny<0||nx>=n||ny>=m)continue;
if(vis[nx][ny])continue;
if(a[nx][ny]=='.')continue;
if(a[nx][ny]!=a[x][y])q.push_back({nx, ny}), dist[nx][ny]=dist[x][y]+1;
else q.push_front({nx, ny}), dist[nx][ny]=dist[x][y];
}
}
cout<<mxd;
return 0;
}
