#include <vector>
#include <utility>
#include <iostream>
#include <string>
#include <deque>
#include <cmath>
using namespace std;
vector<int> dx = { 1, 1, -1, -1 };
vector<int> dy = { 1, -1, 1, -1 };
int main() {
int h, w;
cin >> h >> w;
vector<string> snow(h);
for (int i = 0; i < h; i++) cin >> snow[i];
vector<vector<int>> depth(h, vector<int>(w));
auto inside = [&](int x, int y) {
return 0 <= x && x < w && 0 <= y && y < h && snow[x][y] != '.';
};
int ans = 1;
deque<pair<int, int>> visit;
visit.push_back({ 0, 0 });
depth[0][0] = 1;
while (!visit.empty()) {
auto [ x, y ] = visit.front();
visit.pop_front();
ans = max(ans, depth[x][y]);
for (int i = 0; i < 4; i++) {
int nx = x + dx[i];
int ny = y + dy[i];
if (inside(nx, ny) && depth[nx][ny] == 0) {
if (snow[x][y] == snow[nx][ny]) {
depth[nx][ny] = depth[x][y];
visit.push_front({ nx, ny });
} else {
depth[nx][ny] = depth[x][y] + 1;
visit.push_back({ nx, ny });
}
}
}
}
cout << ans - 1;
return 0;
}
