#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> pii;
void fast() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
}
int main() {
fast();
// freopen("haybales.in", "r", stdin);
// freopen("haybales.out", "w", stdout);
int n, m;
cin >> n >> m;
vector<string> a(n);
vector<vector<bool>> visited(n, vector<bool>(n, false));
vector<vector<int>> dist(n, vector<int>(m, 1));
for (int i = 0; i < n; i++) cin >> a[i];
vector<pii> mv = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
deque<pii> bfs;
visited[0][0] = true;
bfs.push_back({0, 0});
pii cur;
while (bfs.size()) {
cur = bfs.front();
bfs.pop_front();
for (int i = 0; i < mv.size(); i++)
if ((cur.first + mv[i].first >= 0) &&
(cur.first + mv[i].first < n) &&
(cur.second + mv[i].second >= 0) &&
(cur.second + mv[i].second < m) &&
!visited[cur.first + mv[i].first][cur.second + mv[i].second] &&
a[cur.first + mv[i].first][cur.second + mv[i].second] != '.') {
visited[cur.first + mv[i].first][cur.second + mv[i].second] =
true;
dist[cur.first + mv[i].first][cur.second + mv[i].second] =
dist[cur.first][cur.second];
if (a[cur.first][cur.second] ==
a[cur.first + mv[i].first][cur.second + mv[i].second]) {
bfs.push_front(
{cur.first + mv[i].first, cur.second + mv[i].second});
} else {
bfs.push_back(
{cur.first + mv[i].first, cur.second + mv[i].second});
dist[cur.first + mv[i].first][cur.second + mv[i].second]++;
}
}
}
int ans = 0;
for (int i = 0; i < n; i++)
for (int j = 0; j < m; j++) ans = max(dist[i][j], ans);
cout << ans << '\n';
return 0;
}
