#include <iostream>
#include <fstream>
#include <string>
using namespace std;
const int nmax=1005;
string str;
int a[nmax][nmax],st[nmax],t[nmax],u,s[2*nmax],p[2*nmax],sir[nmax];
int n,m,i,j,mx,r,c,num,ch;
int getnum()
{
    num=0;
    while(str[ch]>='0'&&str[ch]<='9')
    {
        num=num*10+str[ch]-'0';
        ch++;
    }
    ch++;
    return num;
}
int main()
{
    ifstream f("dreptpal.in");
    ofstream g("dreptpal.out");
    f>>n>>m;
    s[0]=-2;
    for(i=1;i<=m;i++)
        s[2*i-1]=-1;
    getline(f,str);
    for(i=1;i<=n;i++)
    {
        getline(f,str);ch=0;
       for(j=1;j<=m;j++)
        s[2*j]=getnum();
        r=0,c=0;
        for(j=1;j<=2*m;j++)
            p[j]=0;
        for(j=1;j<=2*m;j++)
        {
            if(j<=r)
                p[j]=min(p[2*c-j],r-j);
            while(j-p[j]>=1&&j+p[j]<=2*m&&s[j-p[j]]==s[j+p[j]])
                p[j]++;
            if(j+p[j]>r)
                r=j+p[j],c=j;
            p[j]--;
        }
        for(j=1;j<=m;j++)
           {a[i][j]=2*(p[2*j]/2)+1;}
    }
    for(j=1;j<=m;j++)
    {
        for(i=1;i<=n;i++)
            sir[i]=a[i][j];
        u=0;st[0]=0;
        for(i=1;i<=n;i++)
        {
            while(u>0&&sir[i]<sir[st[u]])
                u--;
            t[i]=i-st[u];
            u++;
            st[u]=i;
        }
        u=0;st[0]=n+1;
         for(i=n;i>=1;i--)
        {
            while(u>0&&sir[i]<=sir[st[u]])
                u--;
            t[i]+=(st[u]-i-1);
            u++;
            st[u]=i;
            if(t[i]*sir[i]>mx)
               mx=t[i]*sir[i];
        }
    }
    g<<mx;
    return 0;
}