#include <cstdio>
using namespace std;

const char iname[] = "bmatrix.in";
const char oname[] = "bmatrix.out";
const int  MaxN = 202;

int  n, m;
char A[MaxN][MaxN];
int  H[MaxN][MaxN], M1[MaxN][MaxN], M2[MaxN][MaxN];
int  Rez;


#define maxim(a,b) ((a) > (b) ? (a) : (b))

int main(void)
{
	freopen(iname, "r", stdin);
	freopen(oname, "w", stdout);
	int i, j, k;
	int hmin, max;

	scanf("%d %d\n", &n, &m);
	for (i = 1; i <= n; ++i)
		scanf("%s\n", A[i]+1);

	/* de sus in jos */
	for (i = 1; i <= n; ++i)
		for (j = 1; j <= m; ++j)
			H[i][j] = (A[i][j] == '0') ? H[i-1][j] + 1 : 0;
	for (i = 1; i <= n; ++i)
		for (j = 1; j <= m; ++j) {
			for (k = j, max = 0, hmin = MaxN; k > 0; --k) {
				if (hmin > H[i][k])
					hmin = H[i][k];
				if (max < (j-k+1) * hmin)
					max = (j-k+1) * hmin;
			}
			M1[i][j] = max;
			M1[i][m+1] = maxim(M1[i][m+1], maxim(max, M1[i-1][m+1]));
			M1[n+1][j] = maxim(M1[n+1][j], maxim(max, M1[n+1][j-1]));
		}

	/* de jos in sus */
	for (i = n; i >= 1; --i)
		for (j = 1; j <= m; ++j)
			H[i][j] = (A[i][j] == '0') ? H[i+1][j] + 1 : 0;
	for (i = n; i >= 1; --i)
		for (j = m; j >= 1; --j) {
			for (k = j, max = 0, hmin = MaxN; k <= m; ++k) {
				if (hmin > H[i][k])
					hmin = H[i][k];
				if (max < (k-j+1) * hmin)
					max = (k-j+1) * hmin;
			}
			M2[i][j] = max;
			M2[i][0] = maxim(M2[i][0], maxim(max, M2[i+1][0]));
			M2[0][j] = maxim(M2[0][j], maxim(max, M2[0][j+1]));
	}
	
	/* desparte dreptunghiurile pe verticala */
	for (j = 1; j < m; ++j)
		if (Rez < M1[n+1][j] + M2[0][j+1])
			Rez = M1[n+1][j] + M2[0][j+1];
	for (i = 1; i < n; ++i)
		if (Rez < M1[i][m+1] + M2[i+1][0])
			Rez = M1[i][m+1] + M2[i+1][0];
	printf("%d\n", Rez);

	return 0;
}