#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
int dx[4] = {1, -1, 0, 0}, dy[4] = {0, 0, 1, -1};
void solve() {
int n, m;
cin >> n >> m;
vector<string> grid(n);
for (int i = 0; i < n; i++) {
cin >> grid[i];
}
deque<pii> q;
q.push_front({0, 0});
vector<vector<int>> d(n, vector<int>(m));
d[0][0] = 1;
int ans = 1;
while (q.size()) {
pii c = q.front();
q.pop_front();
int x = c.first, y = c.second;
ans = max(ans, d[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 || grid[nx][ny] == '.')
continue;
if (d[nx][ny]) continue;
if (grid[nx][ny] == grid[x][y]) {
d[nx][ny] = d[x][y];
q.push_front({nx, ny});
} else {
d[nx][ny] = d[x][y] + 1;
q.push_back({nx, ny});
}
}
}
cout << ans << "\n";
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
solve();
return 0;
}
