#include<bits/stdc++.h>
using namespace std;
int main() {
cout.tie(nullptr)->sync_with_stdio(false);
int H, W; cin >> H >> W;
vector<string> grid(H);
for (string& S : grid) cin >> S;
vector<vector<int>> mindist(H, vector<int>(W, -1));
deque<array<int, 2>> bfs = {{0, 0}};
vector<int> dx = {1, 0, -1, 0};
vector<int> dy = {0, 1, 0, -1};
auto check = [&](int a, int b) -> bool {
if (a < 0 || a >= H || b < 0 || b >= W || grid[a][b] == '.') return false;
return true;
};
mindist[0][0] = 1;
int res = 0;
while (!bfs.empty()) {
auto [u, v] = bfs.front();
bfs.pop_front();
res = max(res, mindist[u][v]);
for (int d = 0; d < 4; ++d) {
int a = u + dx[d], b = v + dy[d];
if (!check(a, b)) continue;
if (mindist[a][b] == -1) {
int prev = mindist[u][v];
if (grid[u][v] == grid[a][b]) {
mindist[a][b] = prev;
bfs.push_front({a, b});
} else {
mindist[a][b] = 1 + prev;
bfs.push_back({a, b});
}
}
}
}
cout << res << '\n';
}
