#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

int h, w;
string maps[3000];
int dp[3000][3000];

int main() {
	cin >> h >> w;
	REP(i, h) cin >> maps[i];
	
	fill(dp[0], dp[h], INF);
	
	int ans = 0;
	
	REP(i, h) {
		REP(j, w) {
			if (maps[i][j] == '.') dp[i][j] = 0;
			else {
				if (i > 0) chmin(dp[i][j], dp[i - 1][j] + 1);
				else chmin(dp[i][j], 1);
				
				if (j > 0) chmin(dp[i][j], dp[i][j - 1] + 1);
				else chmin(dp[i][j], 1);
				
				if (i > 0 && j > 0) chmin(dp[i][j], dp[i - 1][j - 1] + 1);
			}
			
			chmax(ans, (dp[i][j] + 1) / 2);
		}
	}
	
	cout << ans << endl;
	
	return 0;
}