#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef double db;
typedef string str;

typedef pair<int, int> pi;
typedef pair<ll,ll> pl;
typedef pair<ld,ld> pd;

typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<ld> vd;
typedef vector<str> vs;
typedef vector<pi> vpi;
typedef vector<pl> vpl;

#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)

#define sz(x) (int)x.size()
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define rsz resize
#define ins insert

#define mp make_pair
#define pb push_back
#define eb emplace_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound

const int MOD = 1e9+7; ///Lifehack: +2*MOD
const int NMAX = 2e5+5;
const ll INF = 1e18;
const ld PI = 4*atan((ld)1);

namespace input {
	template<class T> void re(complex<T>& x);
	template<class T1, class T2> void re(pair<T1,T2>& p);
	template<class T> void re(vector<T>& a);
	template<class T, size_t SZ> void re(array<T,SZ>& a);

	template<class T> void re(T& x) { cin >> x; }
	template<class T, class... Ts> void re(T& t, Ts&... ts) {
		re(t); re(ts...);
	}

	template<class T> void re(complex<T>& x) { T a,b; re(a,b); x = cd(a,b); }
	template<class T1, class T2> void re(pair<T1,T2>& p) { re(p.f,p.s); }
	template<class T> void re(vector<T>& a) { F0R(i,sz(a)) re(a[i]); }
	template<class T, size_t SZ> void re(array<T,SZ>& a) { F0R(i,SZ) re(a[i]); }
}

using namespace input;

namespace output {
	void pr(int x) { cout << x; }
	void pr(long x) { cout << x; }
	void pr(ll x) { cout << x; }
	void pr(unsigned x) { cout << x; }
	void pr(unsigned long x) { cout << x; }
	void pr(unsigned long long x) { cout << x; }
	void pr(float x) { cout << x; }
	void pr(double x) { cout << x; }
	void pr(ld x) { cout << x; }
	void pr(char x) { cout << x; }
	void pr(const char* x) { cout << x; }
	void pr(const string& x) { cout << x; }
	void pr(bool x) { pr(x ? "true" : "false"); }
	template<class T> void pr(const complex<T>& x) { cout << x; }

	template<class T1, class T2> void pr(const pair<T1,T2>& x);
	template<class T> void pr(const T& x);

	template<class T, class... Ts> void pr(const T& t, const Ts&... ts) {
		pr(t); pr(ts...);
	}
	template<class T1, class T2> void pr(const pair<T1,T2>& x) {
		pr("{",x.f,", ",x.s,"}");
	}
	template<class T> void pr(const T& x) {
		pr("{"); // const iterator needed for vector<bool>
		bool fst = 1; for (const auto& a: x) pr(!fst?", ":"",a), fst = 0;
		pr("}");
	}

	void ps() { pr("\n"); } // print w/ spaces
	template<class T, class... Ts> void ps(const T& t, const Ts&... ts) {
		pr(t); if (sizeof...(ts)) pr(" "); ps(ts...);
	}

	void pc() { pr("]\n"); } // debug w/ commas
	template<class T, class... Ts> void pc(const T& t, const Ts&... ts) {
		pr(t); if (sizeof...(ts)) pr(", "); pc(ts...);
	}
	#define dbg(x...) pr("[",#x,"] = ["), pc(x);
}
using namespace output;

int n,m,cate,ans;
int M[1005][1005];
bool uz[1005][1005];
int cand[1005][1005];
int dl[]={0,-1,0,1,0};
int dc[]={0,0,1,0,-1};
char x;
pair<int,int>k;
queue<pair<int,int>>coada;
void solve() {
re(n,m);
memset(M,2,sizeof(M));
cin.get();
FOR(i,1,n+1){
FOR(j,1,m+1)
   {re(x);if(x=='#')M[i][j]=1,cate++,coada.push({i,j});else M[i][j]=0;}
cin.get();
}
while(!coada.empty())
     {k=coada.front();
      coada.pop();
      for(int ii=1;ii<=4;ii++)
        if(M[k.f+dl[ii]][k.s+dc[ii]]==0)
           M[k.f+dl[ii]][k.s+dc[ii]]=1,cate++,cand[k.f+dl[ii]][k.s+dc[ii]]=1+cand[k.f][k.s],coada.push({k.f+dl[ii],k.s+dc[ii]});
     if(cate==n*m)
        break;
     }
if(cate==n*m)
  FOR(i,1,n+1)
  FOR(j,1,m+1)
    ans=max(ans,cand[i][j]);
pr(ans);
}

int main() {
	ios_base::sync_with_stdio(false); cin.tie(0);
	int t=1;
    //cin>>t;
  	while(t--)
         solve();
    return 0;

}


Measured memory_bytes: 14208