#include<iostream.h>
#include<stdio.h>
#include<math.h>
long long i,x[1000],y[1000],m,n,j,d,max,a[1000][1000];
int main()
{
	freopen("orase.in","r",stdin);
	freopen("orase.out","w",stdout);
	cin>>m>>n;
	for(i=1;i<=n;i++)
		cin>>x[i]>>y[i];
	for(i=1;i<=n;i++)
		for(j=1;j<=n;j++)
			if(i!=j)
				a[i][j]=abs(x[i]-x[j])+y[i]+y[j];
	for(i=1;i<=n;i++)
		for(j=1;j<=n;j++)
			if(max<a[i][j]) max=a[i][j];
	cout<<max;
	return 0;
}