#include <bits/stdc++.h>
#define int long long
using namespace std;
int X[] = {-1, 1, 0, 0};
int Y[] = {0, 0, 1, -1};
signed main() {
// freopen("cruise.in", "r", stdin);
// freopen("cruise.out", "w", stdout);
int n, m;
cin >> n >> m;
vector <string> c(n);
for (int i = 0; i < n; i++) {
cin >> c[i];
}
deque < pair <int, int> > q;
q.push_back({0, 0});
vector < vector <int> > dist(n, vector <int>(m));
dist[0][0] = 1;
int ans = 1;
while (!q.empty()) {
int vx = q.front().first;
int vy = q.front().second;
q.pop_front();
ans = max(ans, dist[vx][vy]);
for (int i = 0; i < 4; i++) {
int tox = vx + X[i];
int toy = vy + Y[i];
if (tox < 0 || tox >= n || toy < 0 || toy >= m || c[tox][toy] == '.') continue;
if (!dist[tox][toy]) {
if (c[vx][vy] == c[tox][toy]) {
q.push_front({tox, toy});
dist[tox][toy] = dist[vx][vy];
} else {
q.push_back({tox, toy});
dist[tox][toy] = dist[vx][vy] + 1;
}
}
}
}
cout << ans << endl;
}
