#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
/* DEBUGGING */
#ifdef LOCAL
#define dbg(v) \
cerr << "Line(" << __LINE__ << ") -> " << #v << " = " << (v) << endl;
#else
#define dbg(v)
#endif
/* MODULAR OPERATIONS */
#define MOD 998244353
int mul(int x, int y) { return x * 1ll * y % MOD; }
int binpow(int x, int y) {
int z = 1;
while (y) {
if (y % 2 == 1)
z = mul(z, x);
x = mul(x, x);
y /= 2;
}
return z;
}
int inv(int x) { return binpow(x, MOD - 2); }
int divide(int x, int y) { return mul(x, inv(y)); }
/* TYPES */
typedef vector<int> vi;
typedef vector <vector<int>> vvi;
typedef vector<bool> vb;
typedef vector <vector<bool>> vvb;
typedef vector <string> vs;
typedef vector<char> vc;
typedef vector <vector<char>> vvc;
typedef pair<int, int> pii;
typedef vector <pii> vpii;
/* UTILS */
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#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}};
string arr[4005];
int vis[4005][4005];
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int h, w;
cin >> h >> w;
for(int i = 0; i < h; i++) {
for(int j = 0; j < w; j++) {
vis[i][j] = INF;
}
}
for(int i = 0; i < h; i++) {
cin >> arr[i];
}
deque<pii> deq;
deq.pb({0, 0});
vis[0][0] = 1;
int res = -INF;
while(!deq.empty()) {
pii cur = deq.front();
deq.pop_front();
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(arr[adj.fi][adj.se]==arr[cur.fi][cur.se] && vis[adj.fi][adj.se] > vis[cur.fi][cur.se]) {
vis[adj.fi][adj.se] = vis[cur.fi][cur.se];
deq.push_front(adj);
}
}
}
for(int i = 0; i < h; i++) {
for (int j = 0; j < w; j++) {
if(vis[i][j] < INF) res = max(res, vis[i][j]);
}
}
cout << res << endl;
return 0;
}
// DONT GET STUCK IN ONE APPROACH
// ROTATED PREFIX SUM: (x, y) => (x+y, n-x+y)
// NO SMALL VECTORS!!!
