/*
_____ _ _
/ ____| | | | |
| | __ _ __ __ _ ___ ___ _ _ _ __ ___ | |_ __ _| |_ ___
| | |_ | '__/ _` / __/ __| | | | '_ \ / _ \| __/ _` | __/ _ \
| |__| | | | (_| \__ \__ \ |_| | |_) | (_) | || (_| | || (_) |
\_____|_| \__,_|___/___/\__, | .__/ \___/ \__\__,_|\__\___/
__/ | |
|___/|_|
*/
#pragma gcc target ("avx2")
#pragma gcc optimization ("O3")
#pragma gcc optimization ("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
template<class T> using segset = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
#define FOR(i, x, n) for (int i = x; i < n; i++)
#define F0R(i, x, n) for (int i = x; i >= n; i--)
#define TRAV(it, x) for (auto it = x.begin(); it != x.end(); it++)
#define rall(x) x.rbegin(), x.rend()
#define all(x) x.begin(), x.end()
#define sz size
#define pof pop_front
#define pob pop_back
#define pf push_front
#define pb push_back
#define ins insert
#define mp make_pair
#define rz resize
#define rev reverse
#define lb lower_bound
#define ub upper_bound
// fill for 1
// 0x3f3f3f3f for 1e9
#define mem(a, x) memset(a, x, sizeof(a))
using ll = long long;
const int INF = 2e5 + 5;
const int MOD = 1e9 + 7;
// DLRU
const int dx[4] = {1, 0, 0, -1};
const int dy[4] = {0, -1, 1, 0};
/*
*
*/
//
void solve() {
}
int n, m;
char a[4001][4001];
int dist[4001][4001];
deque<pair<int, int>> q;
bool valid(int x, int y) {
return x >= 0 && y >= 0 && x < n && y < m && a[x][y] != '.';
}
int main()
{
std::ios_base::sync_with_stdio(false); cin.tie(0);
// ifstream cin(".in");
// ofstream cout(".out");
// int t;
// cin >> t;
// while (t--) {
// solve();
// }
FOR(i, 0, 4001) {
FOR(j, 0, 4001) {
dist[i][j] = 1e9;
}
}
cin >> n >> m;
FOR(i, 0, n) cin >> a[i];
dist[0][0] = 0;
q.pf(mp(0, 0));
while (q.sz()) {
int x = q.front().first, y = q.front().second;
q.pof();
FOR(i, 0, 4) {
int nx = x + dx[i], ny = y + dy[i];
if (!valid(nx, ny)) continue;
int w = (a[x][y] == a[nx][ny]) ^ 1;
if (dist[x][y] + w < dist[nx][ny]) {
dist[nx][ny] = dist[x][y] + w;
if (w == 1) q.pb(mp(nx, ny));
else q.pf(mp(nx, ny));
}
}
}
// FOR(i, 0, n) {
// FOR(j, 0, m) {
// cerr << dist[i][j] << ' ';
// }
// cerr << '\n';
// }
int ans = 0;
FOR(i, 0, n) {
FOR(j, 0, m) {
if (dist[i][j] == 1e9) continue;
ans = max(ans, dist[i][j]);
}
}
cout << ans + 1 << '\n';
return 0;
}
/*
*
*/
//5 8
//FFR.....
//.FRRR...
//.FFFFF..
//..RRRFFR
//.....FFF
