#include <cstdio>
#include <algorithm>
#include <cstring>
#define MaxN 300
#define INF 2140000000

FILE *IN,*OUT;
int N,M,L[MaxN][MaxN],C[MaxN][MaxN],RL[MaxN][MaxN],RC[MaxN][MaxN];
struct coord{int x,y,Size;}Fwd[MaxN][MaxN],Bkd[MaxN][MaxN];
bool v[MaxN][MaxN];
char Ch;

int min(int a,int b)
{
	if(a<b)
		return a;
	else return b;
}
int max(int a,int b)
{
	if(a>b)
		return a;
	else return b;
}

int main()
{
    IN=fopen("bmatrix.in","r");
    OUT=fopen("bmatrix.out","w");
 
    fscanf(IN,"%d%d ",&N,&M);
    for(int i=1;i<=N;i++)
        for(int j=1;j<=M;j++)
        {
            fscanf(IN,"%c ",&Ch);
            v[i][j]=Ch-'0';
        }
    for(int i=1;i<=N;i++)
        for(int j=1;j<=M;j++)
        {
            if(v[i][j])
                L[i][j]=C[i][j]=0;
            else
            {
                L[i][j]=L[i][j-1]+1;
                C[i][j]=C[i-1][j]+1;
            }
        }
	for(int i=N;i>0;i--)
        for(int j=M;j>0;j--)
        {
            if(v[i][j])
                RL[i][j]=RC[i][j]=0;
            else
            {
                RL[i][j]=RL[i][j+1]+1;
                RC[i][j]=RC[i+1][j]+1;
            }
        }
    for(int i=1;i<=N;i++)
        for(int j=1;j<=M;j++)
        {
            if(v[i][j])
				Fwd[i][j].x=i,Fwd[i][j].y=j,Fwd[i][j].Size=0;
            else
            {
                int Max=INF;
                for(int k=i;k>=i-C[i][j]+1;k--)
                    Max=min(Max,L[k][j]);
                Fwd[i][j].x=i-C[i][j]+1;
                Fwd[i][j].y=j-Max+1;
				Fwd[i][j].Size=C[i][j]*Max;
			}
				if(Fwd[i][j-1].Size>Fwd[i][j].Size)
                    Fwd[i][j]=Fwd[i][j-1];
                if(Fwd[i-1][j].Size>Fwd[i][j].Size)
                    Fwd[i][j]=Fwd[i-1][j];
        }
    for(int i=N;i>0;i--)
        for(int j=M;j>0;j--)
        {
            if(v[i][j])
				Bkd[i][j].x=i,Bkd[i][j].y=j,Bkd[i][j].Size=0;
            else
            {
                int Max=INF;
                for(int k=i;k<=i+RC[i][j]-1;k++)
                    Max=min(Max,RL[k][j]);
                Bkd[i][j].x=i+RC[i][j]-1;
                Bkd[i][j].y=j+Max-1;
				Bkd[i][j].Size=RC[i][j]*Max;
			}
                if(Bkd[i][j+1].Size>Bkd[i][j].Size)
                    Bkd[i][j]=Bkd[i][j+1];
                if(Bkd[i+1][j].Size>Bkd[i][j].Size)
                    Bkd[i][j]=Bkd[i+1][j];
        }
	int Total=0;
	for(int i=1;i<=N;i++)
		for(int j=1;j<=M;j++)
		{
			Total=max(Total,Fwd[i][j].Size+(max(max(Fwd[N][Fwd[i][j].y-1].Size,Fwd[Fwd[i][j].x-1][M].Size),max(Bkd[i+1][1].Size,Bkd[1][j+1].Size))));
		}
	fprintf(OUT,"%d",Total);
    return 0;
}