1 #include <bits/stdc++.h>
2 #define maxn 13003
3 #define _for(i,a,b) for(int i = (a);i < b;i ++)
4 typedef long long ll;
5 using namespace std;
6 inline ll read()
7 {
8 ll ans = 0;
9 char ch = getchar(), last = ' ';
10 while(!isdigit(ch)) last = ch, ch = getchar();
11 while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar();
12 if(last == '-') ans = -ans;
13 return ans;
14 }
15 inline void write(ll x)
16 {
17 if(x < 0) x = -x, putchar('-');
18 if(x >= 10) write(x / 10);
19 putchar(x % 10 + '0');
20 }
21 int n,m;
22 int a[2503][2503];
23 int dp[2503][2503];
24 int h[2503][2503];
25 int d[2503][2503];
26 int main()
27 {
28 n = read(), m = read();
29 _for(i,1,n+1)
30 _for(j,1,m+1)
31 a[i][j] = read();
32
33 for(int i = 1;i < n+1;i ++)
34 {
35 h[i][1] = 0;
36 for(int j = 2;j < m+1;j ++)
37 {
38 if(a[i][j-1]==0)
39 h[i][j] = h[i][j-1]+1;
40 else
41 h[i][j] = 0;
42 }
43 }
44
45 for(int i = 1;i < m+1;i ++)
46 {
47 d[1][i] = 0;
48 for(int j = 2;j < n+1;j ++)
49 {
50 if(a[j-1][i]==0)
51 d[j][i] = d[j-1][i]+1;
52 else
53 d[j][i] = 0;
54 }
55 }
56
57 int rnt = 0;
58
59 _for(i,1,n+1)
60 _for(j,1,m+1)
61 if(a[i][j]==1)
62 dp[i][j] = min(dp[i-1][j-1],min(d[i][j],h[i][j])) + 1,
63 rnt = max(rnt,dp[i][j]);
64
65 memset(h,0,sizeof(h));
66 memset(dp,0,sizeof(dp));
67 for(int i = 1;i < n+1;i ++)
68 {
69 h[i][m] = 0;
70 for(int j = m-1;j > 1;j --)
71 {
72 if(a[i][j+1]==0)
73 h[i][j] = h[i][j+1]+1;
74 else
75 h[i][j] = 0;
76 }
77 }
78
79 _for(i,1,n+1)
80 for(int j = m;j > 0;j --)
81 if(a[i][j]==1)
82 dp[i][j] = min(dp[i-1][j+1],min(d[i][j],h[i][j])) + 1,
83 rnt = max(rnt,dp[i][j]);
84
85 write(rnt);
86 return 0;
87 }
