//
// All truth are easy to understand once they are discovered.
// The point is to discover them
//
#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 123;
int was[4001][4001];
void solve(){
int n, m; cin >> n >> m;
string g[n];
for (int i = 0; i < n; i++) {
cin >> g[i];
}
vector<int> dx = {0, 0, 1, -1};
vector<int> dy = {1, -1, 0, 0};
deque<pair<int, int>> dq;
was[0][0] = 1;
dq.push_front({0, 0});
int ans = 0;
while (!dq.empty()) {
auto [x, y] = dq.front();
dq.pop_front();
ans = max(ans, was[x][y]);
for (int i = 0; i < 4; i++) {
int nx = x + dx[i], ny = y + dy[i];
if (nx >= 0 && nx < n && ny >= 0 && ny < m && g[nx][ny] != '.' && was[nx][ny] == 0) {
if (g[nx][ny] == g[x][y]) {
was[nx][ny] = was[x][y];
dq.push_front({nx, ny});
} else {
was[nx][ny] = was[x][y] + 1;
dq.push_back({nx, ny});
}
}
}
}
cout << ans;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int tt = 1;
// cin >> tt;
while (tt--) {
solve();
cout << '\n';
}
return 0;
}
