#include <bits/stdc++.h>
using namespace std;
#define all(v) v.begin(), v.end()
#define endl '\n'
#define pl(var) " [" << #var << ": " << (var) << "] "
#define ll long long
void solve() {
int n, m; cin >> n >> m;
vector<string> arr(n);
for (int i = 0; i < n; i++) cin >> arr[i];
deque<pair<pair<int, int>, int>> dq;
int ans = 0;
dq.emplace_back(make_pair(0, 0), 0);
vector<vector<bool>> vis(n, vector<bool>(m, 0));
int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};
auto is_within_bounds = [&](int x, int y) {
return x >= 0 && x < n && y >= 0 && y < m;
};
while (dq.size() != 0) {
auto [node, dist] = dq.front();
dq.pop_front();
if (vis[node.first][node.second]) continue;
vis[node.first][node.second] = 1;
ans = max(ans, dist);
int x = node.first;
int y = node.second;
for (int i = 0; i < 4; i++) {
int nx = x + dx[i];
int ny = y + dy[i];
if (is_within_bounds(nx, ny)) {
if (arr[nx][ny] == '.') continue;
if (arr[nx][ny] == arr[x][y]) {
dq.emplace_front(make_pair(nx, ny), dist);
} else {
dq.emplace_back(make_pair(nx, ny), dist + 1);
}
}
}
}
cout << ans + 1 << endl;
}
int main() {
// freopen(".in", "r", stdin);
// freopen(".out", "w", stdout);
ios::sync_with_stdio(false);
cin.tie(nullptr);
int T = 1;
// cin >> T;
while (T--)
solve();
}
