#include <cstdio>
#include <algorithm>

using namespace std;

#define maxn 1010

int n, m, sol, st0, center, mright, left, right;
int v[maxn][maxn], d[maxn][maxn];
int st[maxn], pz[maxn];

int main()
{
    freopen("dreptpal.in", "r", stdin);
    freopen("dreptpal.out", "w", stdout);

    scanf("%d%d", &n, &m);
    for(int i=1; i<=n; ++i)
        for(int j=1; j<=m; ++j)
            scanf("%d", &v[i][j]);

    for(int i=1; i<=n; ++i)
    {
        center=mright=0;
        for(int j=1; j<=m; ++j)
        {
            if(j<=mright)
                d[i][j]=min(d[i][2*center-j], 2*(m-j)+1);
            else
                d[i][j]=1;

            left=j-d[i][j]/2;
            right=j+d[i][j]/2;

            while(v[i][left-1]==v[i][right+1] && left>1 && right<m)
            {
                --left;
                ++right;
                d[i][j]+=2;
            }

            if(right>mright)
            {
                center=j;
                mright=right;
            }
        }
    }

    sol=n;

    for(int i=1; i<=m; ++i)
    {
        st0=0;
        st[0]=0;
        for(int j=1; j<=n+1; ++j)
        {
            while(d[j][i]<st[st0] && st0>0)
            {
                sol=max(sol, (j-pz[st0])*st[st0]);
                --st0;
            }
            if(d[j][i]==st[st0])
                continue;
            st[++st0]=d[j][i];
            pz[st0]=j;
        }
    }

    printf("%d\n", sol);

    return 0;
}