#include <bits/stdc++.h>
#define int long long
using namespace std;
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define sz(a) (int)(a).size()
#define el '\n'
#define F first
#define S second
#define For(i, a, b) for (int i = (a); i <= (int)(b); i++)
#define Rof(i, a, b) for (int i = (a); i >= (int)(b); i--)
#define Fore(it, x) for (auto it = (x).begin(); it != (x).end(); ++it)
using vb = vector<bool>;
using vvb = vector<vb>;
using vc = vector<char>;
using vvc = vector<vc>;
using vi = vector<int>;
using vvi = vector<vi>;
using pii = pair<int, int>;
using vii = vector<pii>;
//*** START CODING ***//
const long long oo = 2e18, mod = 1e9 + 7;
const int ms = 2e5 + 5;
int n, m;
int dx[4] = {0, 0, -1, 1};
int dy[4] = {-1, 1, 0, 0};
void solve() {
cin >> n >> m;
vvc a(n, vc(m));
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cin >> a[i][j];
}
}
vvi dist(n, vi(m, 0));
deque<pii> q;
q.push_back({0, 0});
int ans = 0;
dist[0][0] = 1;
while (!q.empty()) {
pii cur = q.front();
q.pop_front();
ans = max(ans, dist[cur.F][cur.S]);
for (int i = 0; i < 4; i++) {
int nx = cur.F + dx[i];
int ny = cur.S + dy[i];
if (nx < 0 or nx >= n or ny < 0 or ny >= m) continue;
if (a[nx][ny] == '.') continue;
if (dist[nx][ny] != 0) continue;
if (a[cur.F][cur.S] == a[nx][ny]) {
dist[nx][ny] = dist[cur.F][cur.S];
q.push_front({nx, ny});
} else {
dist[nx][ny] = dist[cur.F][cur.S] + 1;
q.push_back({nx, ny});
}
}
}
cout << ans << el;
}
int32_t main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
solve();
return 0;
}
