#include <bits/stdc++.h>
using namespace std;
using lli = long long;
#ifdef LOCAL
#include </home/marcus06/mycp/Library/debug.h>
#else
#define debug(...)
#endif
const int dx[] = {0, 0, -1, 1};
const int dy[] = {-1, 1, 0, 0};
void solve() {
int H, W;
cin >> H >> W;
vector g(H, vector <char> (W));
for (int i = 0; i < H; ++i) {
for (int j = 0; j < W; ++j) {
cin >> g[i][j];
}
}
auto inside = [&](int u, int v) -> bool {
return (u >= 0 && v >= 0 && u < H && v < W);
};
vector depth(H, vector <int> (W));
deque <pair <int, int>> dq;
depth[0][0] = 1;
dq.emplace_back(0, 0);
int ans = 0;
while (!dq.empty()) {
auto [x, y] = dq.front(); dq.pop_front();
ans = max(ans, depth[x][y]);
for (int i = 0; i < 4; ++i) {
int u = x + dx[i], v = y + dy[i];
if (inside(u, v) && g[u][v] != '.' && depth[u][v] == 0) {
depth[u][v] = depth[x][y];
if (g[u][v] == g[x][y]) {
dq.emplace_front(u, v);
} else {
depth[u][v] += 1;
dq.emplace_back(u, v);
}
}
}
}
cout << ans << '\n';
}
int main() {
std::cin.tie(0)->sync_with_stdio(0);
#ifdef LOCAL
auto begin = std::chrono::high_resolution_clock::now();
#endif
int tt = 1;
while (tt--) {
solve();
}
#ifdef LOCAL
auto end = std::chrono::high_resolution_clock::now();
auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);
std::cerr << "Time measured: " << elapsed.count() * 1e-9 << " seconds.\n";
#endif
return 0;
}
