#include <fstream>
#include <cmath>
using namespace std;
ifstream fin("orase.in");
ofstream fout("orase.out");
struct poz
{
    int x,y;
}a[2];
int n,m,s,s1,s2,i,x,y;
int main()
{
    fin>>n>>m;
    fin>>a[0].x>>a[0].y>>a[1].x>>a[1].y;
    s=abs(a[0].x-a[1].x)+a[0].y+a[1].y;
    for(i=1;i<=m-2;i++)
    {
        fin>>x>>y;
        s1=abs(a[0].x-x)+a[0].y+y;
        s2=abs(x-a[1].x)+y+a[1].y;
        if(s1>s2&&s1>s)
        {
            s=s1;
            a[1].x=x;
            a[1].y=y;
        }
        else
        if(s1<s2&&s2>s)
        {
            s=s2;
            a[0].x=x;
            a[0].y=y;
        }
    }
    fout<<s;
    return 0;
}