#include <bits/stdc++.h>
using i64 = long long;
const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, 1, 0, -1};
int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
int h, w;
std::cin >> h >> w;
std::vector<std::string> g(h);
for (auto &s : g) {
std::cin >> s;
}
std::vector dis(h, std::vector<int>(w, -1));
dis[0][0] = 0;
std::deque<std::tuple<int, int>> q;
q.push_back({0, 0});
int ans = 0;
while (q.size()) {
auto [x, y] = q.front();
q.pop_front();
ans = std::max(ans, dis[x][y]);
for (int i = 0; i < 4; i++) {
int tx = x + dx[i];
int ty = y + dy[i];
if (tx < 0 || tx >= h || ty < 0 || ty >= w || g[tx][ty] == '.' || dis[tx][ty] != -1) {
continue;
}
if (g[x][y] == g[tx][ty]) {
dis[tx][ty] = dis[x][y];
q.push_front({tx, ty});
} else {
dis[tx][ty] = dis[x][y] + 1;
q.push_back({tx, ty});
}
}
}
std::cout << 1 + ans << "\n";
return 0;
}
