#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define int long long
using namespace std;
using namespace __gnu_pbds;
template<typename T>
using ordered_multiset = tree<
T,
null_type,
std::less_equal<T>,
rb_tree_tag,
tree_order_statistics_node_update>;
void solve() {
int h, w;
cin >> h >> w;
vector<string> grid(h);
for (int i = 0; i < h; i++) cin >> grid[i];
vector dist(h, vector<int>(w, 0));
deque<pair<int, int>> d;
dist[0][0] = 1;
d.emplace_back(0, 0);
vector<int> dx{0, 0, 1, -1};
vector<int> dy{1, -1, 0, 0};
int res = 0;
while (!d.empty()) {
auto [x, y] = d.front(); d.pop_front();
res = max(res, dist[y][x]);
for (int i = 0; i < 4; i++) {
int _x = x + dx[i], _y = y + dy[i];
if (_x < 0 || _x >= h || _y < 0 || _y >= w || grid[_y][_x] == '.' || dist[_y][_x] != 0) continue;
if (grid[y][x] != grid[_y][_x]) {
dist[_y][_x] = dist[y][x] + 1;
d.emplace_back(_x, _y);
}
else {
dist[_y][_x] = dist[y][x];
d.emplace_front(_x, _y);
}
}
}
cout << res << endl;
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int t = 1;
// cin >> t;
while (t--)
solve();
return 0;
}
