#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/hash_policy.hpp>
#define Add(x, y) (x + y >= mod) ? (x + y - mod) : (x + y)
#define lowbit(x) x & (-x)
#define pi pair<ll, ll>
#define pii pair<ll, pair<ll, ll>>
#define iip pair<pair<ll, ll>, ll>
#define ppii pair<pair<ll, ll>, pair<ll, ll>>
#define ls(k) k << 1
#define rs(k) k << 1 | 1
#define fi first
#define se second
#define full(l, r, x) for(auto it = l; it != r; ++it) (*it) = x
#define Full(a) memset(a, 0, sizeof(a))
#define open(s1, s2) freopen(s1, "r", stdin), freopen(s2, "w", stdout);
#define For(i, l, r) for(register int i = l; i <= r; ++i)
#define _For(i, l, r) for(register int i = r; i >= l; --i)
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
using namespace std;
using namespace __gnu_pbds;
typedef double db;
typedef unsigned long long ull;
typedef long long ll;
bool Begin;
const int N = 3030;
inline ll read(){
    ll x = 0, f = 1;
    char c = getchar();
    while(c < '0' || c > '9'){
        if(c == '-')
          f = -1;
        c = getchar();
    }
    while(c >= '0' && c <= '9'){
        x = (x << 1) + (x << 3) + (c ^ 48);
        c = getchar();
    }
    return x * f;
}
inline void write(ll x){
	if(x < 0){
		putchar('-');
		x = -x;
	}
	if(x > 9)
	  write(x / 10);
	putchar(x % 10 + '0');
}
inline char get(){
	char c;
	while(1){
		c = getchar();
		if(c == '.' || c == '#')
		  break;
	}
	return c;
}
int n, m, ans;
bool f[N][N];
queue<pair<int ,int>> q, Q;
int dx[] = {0, 0, 1, -1}, dy[] = {1, -1, 0, 0};
inline void bfs(){
	while(!q.empty()){
		swap(q, Q);
		while(!Q.empty()){
			int x = Q.front().fi, y = Q.front().se;
//			cerr << x << ' ' << y << '\n';
			Q.pop();
			for(int i = 0; i < 4; ++i){
				int zx = x + dx[i], zy = y + dy[i];
				if(zx < 0 || zx > n + 1 || zy < 0 || zy > m + 1)
				  continue;
				if(!f[zx][zy]){
					f[zx][zy] = 1;
					q.push({zx, zy});
				} 
			}
		}
		++ans;
	}
}
bool End;
int main(){
	n = read(), m = read();
	for(int i = 1; i <= n; ++i){
		for(int j = 1; j <= m; ++j){
			if(get() == '.'){
				q.push({i, j});
				f[i][j] = 1;
			}
		}
	}
	for(int i = 0; i <= m + 1; ++i){
		q.push({0, i});
		q.push({n + 1, i});
		f[0][i] = f[n + 1][i] = 1;
	}
	for(int i = 1; i <= n; ++i){
		q.push({i, 0});
		q.push({i, m + 1});
		f[i][0] = f[i][m + 1] = 1;
	}
	bfs();
	write(ans - 1);
	cerr << '\n' << abs(&Begin - &End) / 1048576 << "MB";
	return 0;
}