#include<stdio.h>
int a[50001],b[50001],n,m,i,j;
int abs(int a)
{if(a<0) return -a;
 return a;}
int main()
{freopen("orase.in","r",stdin);
 freopen("orase.out","w",stdin);
 scanf("%d %d",&n,&m);
 for(i=1;i<=n;i++)
  scanf("%d %d",&a[i],&b[i]);
 unsigned long max=0;
 for(i=1;i<n;i++)
  for(j=i+1;j<=n;j++)
   if(max<b[i]+b[j]+abs(a[j]-a[i]))
   max=b[i]+b[j]+abs(a[j]-a[i]);
 printf("%u",max);
 fclose(stdout);
 return 0;}