#include <cstdio>

#include <iostream>

#define N 2510

#define max(x, y) ((x) > (y) ? (x) : (y))

#define min(x, y) ((x) < (y) ? (x) : (y))

int n, m, ans;

unsigned short up[N][N], left[N][N], right[N][N], f[N][N][2];

bool a[N][N];

inline int read()

{

    int x = 0, f = 1;

    char ch = getchar();

    for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -1;

    for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - '0';

    return x * f;

}

int main()

{

	int i, j;

	n = read();

	m = read();

	for(i = 1; i <= n; i++)

		for(j = 1; j <= m; j++)

		{

			f[i][j][0] = f[i][j][1] = a[i][j] = read();

			up[i][j] = a[i - 1][j] ? 0 : up[i - 1][j] + 1;

			left[i][j] = a[i][j - 1] ? 0 : left[i][j - 1] + 1;

		}

	for(i = 1; i <= n; i++)

		for(j = m; j >= 1; j--)

			right[i][j] = a[i][j + 1] ? 0 : right[i][j + 1] + 1;

	for(i = 1; i <= n; i++)

		for(j = 1; j <= m; j++)

		{

			if(!a[i][j]) continue;

			f[i][j][0] = min(f[i - 1][j - 1][0], min(up[i][j], left[i][j])) + 1;

			f[i][j][1] = min(f[i - 1][j + 1][1], min(up[i][j], right[i][j])) + 1;

			ans = max(ans, max(f[i][j][0], f[i][j][1]));

		}

	printf("%d\n", ans);

	return 0;

}