#include <bits/stdc++.h>

using namespace std;
ifstream fin("orase.in");
ofstream fout("orase.out");


int main()
{
  int n,i,m,x,y,maxim=-1,minim=INT_MAX;
  fin>>m>>n;
  for(i=1;i<=n;i++)
  {
      fin>>x>>y;
      if(x-y<minim) minim=x-y;
      if(x+y>maxim) maxim=x+y;
  }
  fout<<maxim-minim;
    return 0;
}