#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimize("unroll-loops")
#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});
}
}
}
}
vector<int> dist(n*m, -1);
priority_queue<pair<int,int>> p;
p.push({0, 0});
while (p.size()) {
auto [w, v] = p.top();
p.pop();
if (dist[v] != -1) continue;
dist[v] = -w;
for (auto [e, ew]: adj[v]) {
if (dist[e] == -1) {
p.push({w - ew, e});
}
}
}
cout << *max_element(dist.begin(), dist.end()) +1 << '\n';
return 0;
}
