#include<cstdio>
int v[1005][1005];
int p[1005][1005];
int st[1005],dr[1005];
int m;
void extend(int i,int pos)
{
    while(pos-p[i][pos]>0 && pos+p[i][pos]<=m && v[i][pos-p[i][pos]]==v[i][pos+p[i][pos]])
      p[i][pos]++;
}
int main()
{
    freopen("dreptpal.in","r",stdin);
    freopen("dreptpal.out","w",stdout);
    int n,i,j,c;
    scanf("%d%d",&n,&m);
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
            scanf("%d",&v[i][j]);
    for(i=1;i<=n;i++)
        {
        c=1;
        for(j=1;j<=m;j++)
            {
            if (j>c+p[i][c])
                {
                extend(i,j);
                c=j;
                }
            else
                {
                int j2=2*c-j;
                if (j2-p[i][j2]>c-p[i][c])
                    p[i][j]=p[i][j2];
                else
                    {
                    p[i][j]=c+p[i][c]-j;
                    extend(i,j);
                    c=j;
                    }
                }
            if (j+p[i][j]>c+p[i][c])
                c=j;
            }
        }
    int ans=0;
    for(j=1;j<=m;++j)
        {
        p[0][j]=-2000000000;
        for(i=1;i<=n;++i)
            {
            int k=i-1;
            while(p[k][j]>=p[i][j])
                k=st[k];
            st[i]=k;
            }
        p[n+1][j]=-2000000000;
        for(i=n;i>0;--i)
            {
            int k=i+1;
            while(p[k][j]>=p[i][j])
                k=dr[k];
            dr[i]=k;
            if (ans<(dr[i]-st[i]-1)*(2*p[i][j]-1))
                ans=(dr[i]-st[i]-1)*(2*p[i][j]-1);
            }
        }
    printf("%d\n",ans);
return 0;
}