#include <iostream>
#include <deque>
#include <vector>
#include <array>
#include <utility>
const std::array<std::pair<int, int>, 4> DIR = {{{1, 0}, {0, 1}, {-1, 0}, {0, -1}}};
int main() {
int H, W;
std::cin >> H >> W;
using std::vector;
vector<vector<char>> snow(H, vector<char>(W));
for (auto& i : snow) {
for (char& j : i) {
std::cin >> j;
}
}
int ans = 0;
vector<vector<int>> depth(H, vector<int>(W));
depth[0][0] = 1;
std::deque<std::pair<int, int>> bfs{{0, 0}};
while (!bfs.empty()) {
int x = bfs.front().first, y = bfs.front().second;
bfs.pop_front();
ans = std::max(ans, depth[x][y]);
for (const auto& [dx, dy] : DIR) {
int nx = x + dx, ny = y + dy;
if (nx < 0 || nx == H || ny < 0 || ny == W || snow[nx][ny] == '.' || depth[nx][ny] != 0) {
continue;
}
if (snow[nx][ny] == snow[x][y]) {
bfs.emplace_front(nx, ny);
depth[nx][ny] = depth[x][y];
}
else {
bfs.emplace_back(nx, ny);
depth[nx][ny] = depth[x][y] + 1;
}
}
}
std::cout << ans << "\n";
}
