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

struct Punct{
    int x,y;
};
    ifstream f("hambar.in");
    ofstream g("hambar.out");
int Amax=0,n,m;
Punct a[1001];

int aria(int x1,int y1,int x2,int y2)
{
    return (x2-x1+1)*(y2-y1+1);
}
void citire(int &n,int &m,Punct a[])
{
    f>>n>>m;
    for(int i=1;i<=m;i++)
    {
        f>>a[i].x>>a[i].y;
        cout<<a[i].x<<" "<<a[i].y<<'\n';
    }
}
int cauta(int x1,int y1,int x2,int y2,int k)
{
    while(k<=m){
        if((x1<=a[k].x && a[k].x<=x2)&&(y1<=a[k].y && a[k].y<=y2))
        {
            return k;
        }
        else
        {
            k++;
        }
    }
    return 0;
}


void divide_h(int x1,int y1,int x2,int y2,int k)
{
    int valid=1,ar;
    ar=aria(x1,y1,x2,y2);
    k=cauta(x1,y1,x2,y2,k);
    if((k!=0)&&(Amax<ar))
    {
            divide_h(x1,y1,x2,a[k].y-1,k+1);
            divide_h(x1,y1,a[k].x-1,y2,k+1);
            divide_h(x1,a[k].y+1,x2,y2,k+1);
            divide_h(a[k].x+1,y1,x2,y2,k+1);
    }
    if(k==0){
        Amax=max(Amax,ar);
    }
}
int main()
{
    citire(n,m,a);
    divide_h(1,1,n,n,1);
    g<<Amax;
    return 0;
}