#include <bits/stdc++.h>
using namespace std;
const int mn = 4000;
int vvi[mn][mn];
char vs[mn][mn + 1];
int n, m;
int ct = 0;
vector<pair<int, int>> newones, new2;
signed main() {
// cin.tie(0)->sync_with_stdio(0);
cin >> n >> m;
for (int i = 0; i < n; i++)
cin >> vs[i];
deque<array<int, 3>> dai3;
dai3.push_back({1, 0, 0});
const int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};
while (!dai3.empty()) {
auto [w, x, y] = dai3.front();
dai3.pop_front();
if (vvi[x][y] != 0) {
continue;
}
vvi[x][y] = w;
for (int i = 0; i < 4; i++) {
int nx = x + dx[i], ny = y + dy[i];
if (nx >= 0 && nx < n && ny >= 0 && ny < m) {
if (vvi[nx][ny] == 0 && vs[nx][ny] != '.') {
if (vs[nx][ny] == vs[x][y]) {
dai3.push_front({w, nx, ny});
} else {
dai3.push_back({w + 1, nx, ny});
}
}
}
}
}
int maxi = 0;
for (auto &a : vvi)
for (auto b : a)
maxi = max(maxi, b);
cout << maxi << "\n";
}
