#include <bits/stdc++.h>
using namespace std;
void dbg_out() { cerr << endl; }
template<typename Head, typename... Tail>
void dbg_out(Head H, Tail... T) { cerr << ' ' << H; dbg_out(T...); }
#define dbg(...) cerr << "(" << #__VA_ARGS__ << ")", dbg_out(__VA_ARGS__)
#define endl '\n'
#define int long long
const int MOD = 1e9 + 7;
const int INF = LLONG_MAX >> 1;
string a[4000];
int depth[4000][4000];
int dx[4] = {1, -1, 0, 0}, dy[4] = {0, 0, 1, -1};
void solve() {
int n, m; cin >> n >> m;
for (int i = 0; i < n; i++) {
cin >> a[i];
}
int ans = 0;
deque<pair<int, int>> q;
q.push_back({0, 0});
depth[0][0] = 1;
while (!q.empty()) {
pair<int, int> c = q.front(); q.pop_front();
int x = c.first, y = c.second;
ans = max(ans, depth[x][y]);
for (int i = 0; i < 4; i++) {
int nx = x + dx[i], ny = y + dy[i];
if (0 <= nx && nx < n && 0 <= ny && ny < m && a[nx][ny] != '.' && depth[nx][ny] == 0) {
if (a[x][y] == a[nx][ny]) {
depth[nx][ny] = depth[x][y];
q.push_front({nx, ny});
} else {
depth[nx][ny] = depth[x][y] + 1;
q.push_back({nx, ny});
}
}
}
}
cout << ans << '\n';
}
int32_t main() {
ios::sync_with_stdio(false);
cin.tie(NULL);
int tc = 1;
// cin >> tc;
while (tc--) solve();
}
