#include<cstdio>#include<cstring>#include<cctype>#include<algorithm>using namespace std;#define rep(i,s,t) for(int i=s;i<=t;i++)#define dwn(i,s,t) for(int i=s;i>=t;i--)int read(){	int x=0;char c=getchar();	while(!isdigit(c)) c=getchar();	while(isdigit(c)) x=x*10+c-‘0‘,c=getchar();	return x;}const int nmax=505;int a[nmax][nmax];void maxs(int &a,int b){	if(a<b) a=b;}int main(){	int m=read(),n=read();	rep(i,1,n) rep(j,1,m) a[i][j]=read(),a[i][j]+=a[i-1][j];	int ans=0,cnt;	rep(i,1,n) rep(j,i,n) {		cnt=0;		rep(k,1,m){		    if(a[j][k]-a[i-1][k]!=j-i+1) maxs(ans,cnt*(j-i+1)),cnt=0;		    else cnt++;	    }	    maxs(ans,cnt*(j-i+1));	}	printf("%d\n",ans);	return 0;}