#include<fstream.h>
#include<math.h>
long s,s1,s2,a,b,i,m,n;
struct orase
		 {long x,y;};
orase o[2];
int main ()
{
ifstream f("orase.in");
ofstream g("orase.out");
f>>n>>m;
f>>o[0].x>>o[0].y;
f>>o[1].x>>o[1].y;
s=abs(o[0].x-o[1].x)+o[0].y+o[1].y;
for (i=0;i<m-2;i++)
	 {f>>a>>b;
	  s1=abs(o[0].x-a)+o[0].y+b;
	  s2=abs(o[1].x-a)+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;}
	 }
g<<s;
return 0;
}