#include <bits/stdc++.h>
using i64 = long long;
constexpr int dx[] = {0, 0, -1, 1};
constexpr int dy[] = {1, -1, 0, 0};
int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
int h, w;
std::cin >> h >> w;
std::vector<std::string> a(h);
for (int i = 0; i < h; i++) {
std::cin >> a[i];
}
auto valid = [&](int x, int y) {
return 0 <= x && x < h && 0 <= y && y < w && a[x][y] != '.';
};
std::vector dist(h, std::vector<int>(w));
dist[0][0] = 1;
int ans = 0;
std::deque<std::pair<int, int>> que;
que.emplace_front(0, 0);
while (!que.empty()) {
auto [x, y] = que.front();
que.pop_front();
ans = std::max(ans, dist[x][y]);
for (int k = 0; k < 4; k++) {
int x1 = x + dx[k], y1 = y + dy[k];
if (valid(x1, y1) && !dist[x1][y1]) {
if (a[x][y] == a[x1][y1]) {
dist[x1][y1] = dist[x][y];
que.emplace_front(x1, y1);
} else {
dist[x1][y1] = dist[x][y] + 1;
que.emplace_back(x1, y1);
}
}
}
}
std::cout << ans << '\n';
return 0;
}
