#include<bits/stdc++.h>
using namespace std;
const int M = 1100;
int n, m, ans = 0;
int c;
int mp[M][M];
int l[M][M], r[M][M], up[M][M];
int b[M][M];
int main() {
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	cin >> n >> m;
	for(int i = 1; i <= n; i ++)
		for(int j = 1; j <= m; j ++) {
			cin >> c;
			b[i][j] = b[i - 1][j] + b[i][j - 1] - b[i - 1][j - 1] + c;
			if(c) mp[i][j] = 1;
			l[i][j] = r[i][j] = j;
			up[i][j] = 1;
		}
	for(int i = 1; i <= n; i ++)
		for(int j = 1; j <= m; j ++)
			if(mp[i][j] && mp[i][j - 1])
				l[i][j] = l[i][j - 1];
	for(int i = 1; i <= n; i ++)
		for(int j = m; j >= 1; j --)
			if(mp[i][j] && mp[i][j + 1])
				r[i][j] = r[i][j + 1];
	for(int i = 1; i <= n; i ++)
		for(int j = 1; j <= m; j ++) {
			if(mp[i][j] && mp[i - 1][j]) {
				up[i][j] = up[i - 1][j] + 1;
				r[i][j] = min(r[i][j], r[i - 1][j]);
				l[i][j] = max(l[i][j], l[i - 1][j]);
			}
			int x = i, y = r[i][j];
			int x1 = i - up[i][j], y1 = l[i][j] - 1;
			ans = max(ans, b[x][y] - b[x][y1] - b[x1][y] + b[x1][y1]);
		}
	cout << ans;
	return 0;
}