#define debug_interval ','
#define dump_interval ' '
#define debug_toggle 1
//{
#include<bits/stdc++.h>
using namespace std;
#define hi cerr<<"hi"<<endl;
#define int long long
#define INT_MAX LLONG_MAX
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define pb push_back
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define fi first
#define se second
#define mp make_pair
#define rev reverse
#define dans dump(ans)
#define MOD 1000000007
#define amp(v,n) (v).count(n)?v[n]++:v[n]=1
#define sysp system("pause")
#define PI acos(-1)
#define pf push_front
#define ins insert

//{
inline int toInt(string s){int v;istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x){ostringstream sout;sout<<x;return sout.str();}
template<class...A> inline void dump(){cout<<endl;}
template<class...A> inline void dump_rest() {cout<<endl;}
template<class T, class...A> inline void dump_rest(const T& first, const A&... rest){cout<<dump_interval<<first;dump_rest(rest...);}
template<class T,class...A> inline void dump(const T&first,const A&...rest){cout<<first;dump_rest(rest...);}
template<class...A> inline void debug(){cerr<<endl;}
template<class...A> inline void debug_rest() {cerr<<endl;}
template<class T, class...A> inline void debug_rest(const T& first, const A&... rest){cerr<<debug_interval<<first;debug_rest(rest...);}
template<class T,class...A> inline void debug(const T&first,const A&...rest){if(debug_toggle)cerr<<first,debug_rest(rest...);}
unsigned XorShift(void){static unsigned x = 123456789;static unsigned y = 362436069;static unsigned z = 521288629;static unsigned w = 88675123;unsigned t;t = x ^ (x << 11);x = y; y = z; z = w;return w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));}
//}

typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;

template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}
template<int m>class mint{private:int i;public:mint() : i(0){}mint(int i): i((i%m+m)%m){}mint operator+(const mint& o){return o.i+i;}mint operator*(const mint& o){return o.i*i;}mint operator-(){return -i;}operator int() {return i;}};

//}

int ans;
int h,w;
char a[1111][1111];
int mem[1111][1111];
int dy[4]={-1,0,1,0},dx[4]={0,1,0,-1};

bool c(int y,int x){
	return y>=0&&x>=0&&y<h&&x<w;
}

int solve(){
	int ret=0;
	queue<pint> q[2];
	rep(i,h){
		rep(j,w){
			if(a[i][j]=='#'&&mem[i][j]==0){
				q[0].push({i,j});
				mem[i][j]=1;
			}
		}
	}
	while(true){
		if(q[0].empty()&&q[1].empty())break;
		int cnt=0;
		if(ret%2==0){
			while(!q[0].empty()){
				pint p;p=q[0].front();q[0].pop();
				int y=p.fi,x=p.se;
				rep(i,4){
					int ny=y+dy[i],nx=x+dx[i];
					if(c(ny,nx)&&mem[ny][nx]==0){
						mem[ny][nx]=1;
						q[1].push({ny,nx});
						cnt++;
					}
				}
			}
		}
		if(ret%2==1){
			while(!q[1].empty()){
				pint p;p=q[1].front();q[1].pop();
				int y=p.fi,x=p.se;
				rep(i,4){
					int ny=y+dy[i],nx=x+dx[i];
					if(c(ny,nx)&&mem[ny][nx]==0){
						mem[ny][nx]=1;
						q[0].push({ny,nx});
						cnt++;
					}
				}
			}
		}
		ret++;
	}
	return ret;
}

main(){
	cin>>h>>w;
	rep(i,h){
		rep(j,w){
			cin>>a[i][j];
		}
	}
	dump(solve()-1);
}





Measured memory_bytes: 27316