#include<cstdio>
#include<iostream>
using namespace std;

FILE *f = fopen("dreptpal.in", "r");
FILE *g = fopen("dreptpal.out", "w");

#define MaxN 1010

int N, M, Sol;
int A[MaxN][MaxN], B[MaxN][MaxN];

void citire(void)
{
    fscanf (f, "%d %d", &N, &M);
    for (int i=1;i<=N;i++)
        for (int j=1;j<=M;j++)
            fscanf (f, "%d ", &A[i][j]);
}

void aflarePalindromLinie(void)
{
    for (int i=1;i<=N;i++)
    {
        A[i][0] = -1;

        int dr = 0, pivot = 0;
        for (int j=1;j<=M;j++)
        {
            int known = dr > j ? min (B[i][(pivot << 1) - j]>>1, dr - j) : 1;

            for (;A[i][j - known] == A[i][j + known]; ++ known);

            if (dr <= j + known)
                dr = j + known,
                pivot = j;

            B[i][j] = (known << 1) - 1;
        }
    }
}

int Stiva[MaxN], varf, Poz[MaxN];

void aflareCuStiva(void)
{
    ++ N;

    for (int j=1;j<=M;j++)
    {
        Stiva[varf = 1] = B[1][j];
        Poz[varf] = 1;

        for (int i=2;i<=N;i++)
        {
            while (varf && Stiva[varf] > B[i][j])
                Sol = max (Sol, Stiva[varf] * (i - Poz[--varf] - 1));

            Stiva[++varf] = B[i][j];
            Poz[varf] = i;
        }
        
        Stiva[varf = 1] = B[N-1][j];
        Poz[varf] = N-1;

        for (int i=N-2;i>=0;i--)
        {
            while (varf && Stiva[varf] > B[i][j])
                Sol = max (Sol, Stiva[varf] * (Poz[--varf] - i - 1));

            Stiva[++varf] = B[i][j];
            Poz[varf] = i;
        }
    }
}

int main()
{
    citire();
    aflarePalindromLinie();
    aflareCuStiva();
    
    fprintf (g, "%d", Sol);
}