#include <bits/stdc++.h>
using namespace std;
using ll = long long;
signed main() {
cin.tie(0)->sync_with_stdio(0);
int n, m;
cin >> n >> m;
vector<string> mat(n);
for (string& s : mat) {
cin >> s;
}
auto id = [m](int i, int j) { return i* m + j;};
vector<vector<pair<int,int>>> adj(n * m);
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
for (auto [di, dj] : {pair{0, -1}, {0, 1}, {-1, 0}, {1, 0}}) {
int ni = i + di;
int nj = j + dj;
if (clamp(ni, 0,n-1) == ni && clamp(nj, 0, m-1) == nj) {
if (mat[ni][nj] == '.' || mat[i][j] == '.') continue;
int c = mat[i][j] != mat[ni][nj];
adj[id(i, j)].push_back({id(ni, nj), c});
}
}
}
}
static constexpr int inf = 1e9;
vector<int> dist(n*m, inf), vis(n*m, 0);
queue<int> cur, next;
dist[0] = 0;
cur.push(0);
int res = 0;
while (cur.size()) {
int v = cur.front();
vis[v] = 1;
res = max(res, dist[v]);
for (auto [e, ec]: adj[v]) {
if (vis[e]) continue;
dist[e] = min(dist[e], dist[v] + ec);
if (ec) next.push(e);
else cur.push(e);
}
cur.pop();
if (cur.empty()) {
cur.swap(next);
next = {};
}
}
cout << res+1 << '\n';
return 0;
}
