#include <bits/stdc++.h>
using namespace std;
#define int long long // Keep for main logic
#define all(x) (x).begin(), (x).end()
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> pi;
#define f first
#define s second
#define pb push_back
#define endl "\n"
const int N = 4005;
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, 1, 0, -1};
int n, m;
vector<string> snow;
vector<vector<int>> depth; // Use dynamic allocation
bool inside(int x, int y) {
return (x >= 0 && x < n && y >= 0 && y < m && snow[x][y] != '.');
}
void solve() {
cin >> n >> m;
snow.assign(n, ""); // Resize snow vector
depth.assign(n, vector<int>(m, 0)); // Dynamically allocate depth
for (int i = 0; i < n; i++) {
cin >> snow[i];
}
int ans = 0;
deque<pi> dq;
if (inside(0, 0)) {
dq.push_back({0, 0});
depth[0][0] = 1;
}
while (!dq.empty()) {
auto [x, y] = dq.front();
dq.pop_front();
ans = max(ans, depth[x][y]);
for (int i = 0; i < 4; i++) {
int newx = x + dx[i], newy = y + dy[i];
if (inside(newx, newy) && depth[newx][newy] == 0) {
if (snow[x][y] == snow[newx][newy]) {
depth[newx][newy] = depth[x][y];
dq.push_front({newx, newy});
} else {
depth[newx][newy] = depth[x][y] + 1;
dq.push_back({newx, newy});
}
}
}
}
cout << ans << endl;
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
return 0;
}
