#include<fstream>
using namespace std;
ifstream f("orase.in");
ofstream g("orase.out");
int s, s1, s2, a, b, i, m, n, ca;

struct orase{
	long x,y;
};
orase o[2];

int main(){
	f>>n>>m;
	f>>o[0].x>>o[0].y;
	f>>o[1].x>>o[1].y;
	if(o[0].x>o[1].x)
		ca=o[0].x-o[1].x;
	else
		ca=o[1].x-o[0].x;
	s=ca+o[0].y+o[1].y;
	for(i=0; i<m-2; i++)
	{
		f>>a>>b;
		if(o[0].x>a)
			ca=o[0].x-a;
		else
			ca=a-o[0].x;
		s1=ca+o[0].y+b;
		if(o[1].x>a)
			ca=o[1].x-a;
		else
			ca=a-o[1].x;
		s2=ca+o[1].y+b;
		if(s1>s2 && s1>s)
		{
			o[1].x=a;
			o[1].y=b;
			s=s1;
		}
		if(s1<s2 && s2>s)
		{
			o[0].x=a;
			o[0].y=b;
			s=s2;
		}
	}
	f.close();
	g<<s<<"\n";
	g.close();
	return 0;
}