#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
/* TYPES */
typedef pair<int, int> pii;
typedef vector <pii> vpii;
#define pb push_back
#define endl "\n"
#define fi first
#define se second
#define INF 1e6
vpii dirs = {{-1, 0}, {1, 0}, {0, 1}, {0, -1}};
int h, w;
string arr[4000];
int vis[4000][4000];
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> h >> w;
for(int i = 0; i < h; i++) {
for(int j = 0; j < w; j++) vis[i][j] = INF;
cin >> arr[i];
}
deque<pii> deq;
deq.pb({0, 0});
vis[0][0] = 0;
int res = 1;
while(!deq.empty()) {
pii cur = deq.front();
deq.pop_front();
res = max(res, vis[cur.fi][cur.se]);
for(pii& dir: dirs) {
pii adj = {cur.fi+dir.fi, cur.se+dir.se};
if(adj.fi < 0 || adj.fi >= h || adj.se < 0 || adj.se >= w) continue;
if(arr[adj.fi][adj.se] == '.') continue;
if(arr[adj.fi][adj.se]!=arr[cur.fi][cur.se] && vis[adj.fi][adj.se] > vis[cur.fi][cur.se] + 1) {
vis[adj.fi][adj.se] = vis[cur.fi][cur.se] + 1;
deq.push_back(adj);
} else if(vis[adj.fi][adj.se] > vis[cur.fi][cur.se]) {
vis[adj.fi][adj.se] = vis[cur.fi][cur.se];
deq.push_front(adj);
}
}
}
cout << res+1 << endl;
return 0;
}
// DONT GET STUCK IN ONE APPROACH
// ROTATED PREFIX SUM: (x, y) => (x+y, n-x+y)
// NO SMALL VECTORS!!!
