#include <fstream>
#include <vector>
#include <algorithm>
#include <math.h>
#include <utility>
using namespace std;
ifstream fin("orase.in");
ofstream fout("orase.out");
int i,m,n,x,y,a,b,s1,s2,s,c,d;
vector<pair <int, int> > v[50001];
vector<pair <int, int> >::iterator ii,ii2;
int main()
{
    fin>>n>>m;
    fin>>x>>y;
    v[0].push_back(make_pair(x,y));
    ii=v[0].begin();

    fin>>x>>y;
    v[1].push_back(make_pair(x,y));
    ii2=v[1].begin();
    for(i=0;i<m-2;i++)
    {
        fin>>a>>b;
        x=ii->first;
        y=ii->second;
        c=ii2->first;
        d=ii2->second;
        s1=abs(x-a)+y+b;
        s2=abs(c-a)+d+b;
        if(s1>s2 && s1>s)
        {
            c=a;
            d=b;
            s=s1;
        }
        if(s1<s2 && s2>s)
        {
            x=a;
            y=b;
            s=s2;
        }
    }
    fout<<s;
    return 0;
}