#include <bits/stdc++.h>
#include <atcoder/all>
#include <boost/polygon/point_data.hpp>
#include <boost/polygon/voronoi.hpp>
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define all(x) begin(x),end(x)
#define sz(x) (int)(x).size()
using namespace std;
using namespace atcoder;
using ll=long long;
using ld=long double;
using vll=vector<ll>;
using vvll=vector<vll>;
using vi=vector<int>;
using vvi=vector<vi>;
using pll=pair<ll,ll>;
using pi=pair<int,int>;

// using mint=modint998244353;

// using BoostPoint=boost::polygon::point_data<int>;
// using Voronoi=boost::polygon::voronoi_diagram<double>;

int main()
{
  	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int H,W;
	cin>>H>>W;
	vector<string>S(H);
	rep(i,0,H)cin>>S[i];
	vvi dp(H+1,vi(W+1,0));
	int L=0;
	rep(i,1,H+1){
		rep(j,1,W+1){
			if(S[i-1][j-1]=='.')continue;
			dp[i][j]=1+min({dp[i-1][j],dp[i][j-1],dp[i-1][j-1]});
			L=max(L,dp[i][j]);
		}
	}
	cout<<(L+1)/2<<'\n';
}