#include <bits/stdc++.h>
using namespace std;
int main() {
cin.tie(0)->sync_with_stdio(0);
int n, m;
cin >> n >> m;
vector<string> vs(n);
for (auto &a : vs)
cin >> a;
vector<vector<int>> vvi(n, vector<int>(m, -1));
priority_queue<array<int, 3>> pqai3;
pqai3.push({-1, 0, 0});
const int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};
while (!pqai3.empty()) {
auto [w, x, y] = pqai3.top();
pqai3.pop();
w = -w;
if (vvi[x][y] != -1) {
continue;
}
vvi[x][y] = w;
// cout << x << " " << y << " " << w << "\n";
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] == -1 && vs[nx][ny] != '.') {
if (vs[nx][ny] == vs[x][y])
pqai3.push({-w, nx, ny});
else
pqai3.push({-w - 1, nx, ny});
}
}
}
}
int maxi = 0;
for (auto &a : vvi)
for (auto b : a)
maxi = max(maxi, b);
cout << maxi << "\n";
}
