#include <fstream>
#include <cstring>
using namespace std;

ifstream f("dreptpal.in");
ofstream g("dreptpal.out");

int n,m,i,j,v[1001][1001],fr[1001];
int c,sol=0,k,l,lmax;
bool ex;
int main () {
    f >> n >> m;
    for (i=1;i<=n;i++)
        for (j=1;j<=m;j++) f >> v[i][j];
    for (c=2;c<m;c++) {
        i=c;j=c;ex=true;memset(fr,0,sizeof(fr));
        while (i>0 && j<=m && ex==true) {
            ex=false;k=0;
            for (l=1;l<=n;l++)
                if (v[l][i]==v[l][j] && fr[l]==0) {
                    ex=true;
                    k++;
                }
                else {
                    sol=max(sol,(j-i+1)*k);
                    k=0;fr[l]=1;
                }
            sol=max(sol,(j-i+1)*k);
            i--;j++;
        }
    }
    g << sol << '\n';
    f.close();g.close();
    return 0;
}