/**
* Author: wannaStayWithU
* Date: 2/2/2569
*/
#include <bits/stdc++.h>
using namespace std;
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
int n, m;
cin >> n >> m;
char arr[n][m];
int dp[n][m];
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cin >> arr[i][j];
dp[i][j] = 1e9;
}
}
dp[0][0] = 1;
deque<pair<int, int>> qu;
qu.push_front({0, 0});
int di[4] = {1, -1, 0, 0};
int dj[4] = {0, 0, -1, 1};
while (qu.size())
{
auto [u, v] = qu.front();
qu.pop_front();
for (int p = 0; p < 4; p++) {
int du = u + di[p];
int dv = v + dj[p];
if (du < 0 || du >= n || dv < 0 || dv >= m) continue;
if (arr[du][dv] == '.' || dp[du][dv] != 1e9) continue;
if (arr[du][dv] == arr[u][v]) dp[du][dv] = dp[u][v], qu.push_front({du, dv});
else dp[du][dv] = dp[u][v] + 1, qu.push_back({du, dv});
}
}
int ans = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (dp[i][j] != 1e9) ans = max(ans, dp[i][j]);
}
}
cout << ans;
return 0;
}
/*
*/
