#include <bits/stdc++.h>
using namespace std;
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};
int h, w;
vector<string> tracks;
bool inside(int x, int y) {
return (x > -1 && x < h && y > -1 && y < w && tracks[x][y] != '.');
}
int main() {
cin >> h >> w;
tracks.resize(h);
for (int i = 0; i < h; i++) {
cin >> tracks[i];
}
deque<pair<int, int>> edges;
vector<vector<int>> depth(h, vector<int>(w));
edges.push_back({0, 0});
depth[0][0] = 1;
int ans = 0;
while (!edges.empty()) {
auto c = edges.front();
edges.pop_front();
ans = max(ans, depth[c.first][c.second]);
for (int i = 0; i < 4; i++) {
int x = c.first + dx[i], y = c.second + dy[i];
if (!inside(x, y) || depth[x][y] != 0) continue;
if (tracks[x][y] == tracks[c.first][c.second]) {
depth[x][y] = depth[c.first][c.second];
edges.push_front({x, y});
}
else {
depth[x][y] = depth[c.first][c.second] + 1;
edges.push_back({x, y});
}
}
}
cout << ans;
}
