#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define ff first
#define ss second
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define lb lower_bound
#define ub upper_bound
#define setbits(x) __builtin_popcountll(x)
#define zrobits(x) __builtin_ctzll(x)
#define sz(v) (int)v.size()
#define ps(y) cout << fixed << setprecision(y)
#define ms(arr, v) memset(arr, v, sizeof(arr))
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define trav(x, v) for(auto &x: v)
#define w(t) int t; cin >> t; while(t--)
#define rep(i, a, b) for(int i = a; i <= b; i++)
#define rrep(i, a, b) for(int i = a; i >= b; i--)
#define rep0(i, n) rep(i, 0, n - 1)
#define rrep0(i, n) rrep(i, n - 1, 0)
#define rep1(i, n) rep(i, 1, n)
#define rrep1(i, n) rrep(i, n, 1)
#define inp(arr, n) rep0(i, n) cin >> arr[i];
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pii;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<pii> vp;
typedef vector<bool> vb;
typedef vector<string> vs;
typedef map<ll, ll> mii;
typedef map<char, ll> mci;
typedef priority_queue<ll> pq_mx;
typedef priority_queue<ll, vi, greater<>> pq_mn;
typedef tree<ll, null_type, less<>, rb_tree_tag, tree_order_statistics_node_update> pbds;
/*
* find_by_order(i) -> returns an iterator to the element at ith position (0 based)
* order_of_key(i) -> returns the position of element i (0 based)
*/
const int N = 4e3 + 5;
const int mod = 1e9 + 7;
//const int mod = 998244353;
const ll inf = 1e18;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
void fio() {
ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
}
int n, m, dist[N][N];
string a[N];
int dx[] = {-1, 1, 0, 0};
int dy[] = {0, 0, -1, 1};
bool valid(int x, int y) {
return x >= 0 and y >= 0 and x < n and y < m;
}
int main() {
fio();
cin >> n >> m;
rep0(x, n) cin >> a[x];
queue<pii> q;
int mx = 1;
q.emplace(0, 0), dist[0][0] = 1;
while (!q.empty()) {
auto[i, j] = q.front();
q.pop(), mx = max(mx, dist[i][j]);
rep0(d, 4) {
int x = i + dx[d], y = j + dy[d];
if (valid(x, y) and a[x][y] != '.' and dist[x][y] == 0) {
int l = (a[x][y] != a[i][j]);
dist[x][y] = l + dist[i][j], q.emplace(x, y);
}
}
}
cout << mx;
return 0;
}
