#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;
#define F first
#define S second
#define allv(v) v.begin(), v.end()
#define alla(a, N) a, a + N
inline void fastIO() {
cin.tie(nullptr) -> sync_with_stdio(false);
}
const int dx[4] = { 0, 1, 0, -1};
const int dy[4] = { 1, 0, -1, 0};
const int arraysize = 5005;
char grid[arraysize][arraysize];
bool vis[arraysize][arraysize];
int dis[arraysize][arraysize];
inline string YNEOS(bool b) {
return b ? "YES" : "NO";
}
inline string YNeos(bool b) {
return b ? "Yes" : "No";
}
void solve() {
int N, M; cin >> N >> M;
for (int i = 0; i < N; ++i)
for (int j = 0; j < M; ++j)
cin >> grid[i][j];
int mx = 0;
deque<pair<pii, int>> q;
// {{i, j}, dis}
q.emplace_front(pii{0, 0}, 1);
dis[0][0] = 0, vis[0][0] = true;
while (!q.empty()) {
auto [p, d] = q.front();
auto &[i, j] = p; q.pop_front();
mx = max(mx, (dis[i][j] = d));
for (int k = 0; k < 4; ++k) {
int x = i + dx[k], y = j + dy[k];
if (x < 0 || x >= N) continue;
if (y < 0 || y >= M) continue;
if (grid[x][y]=='.') continue;
if (vis[x][y]==true) continue;
vis[x][y] = true;
if (grid[x][y] == grid[i][j])
q.emplace_front(pii{x, y}, d);
else q.emplace_back(pii{x, y}, d+1);
}
}
cout << mx << '\n';
}
int main() {
fastIO();
solve();
}
