#include<stdio.h>
long int n,i,j,k,a[100002],b[100002],aux,max[100002];
void hd(long int ic,long int nc);
void sh(long int i1,long int i2);
long int cauta(long int st,long int dr);
int main()
{
	FILE *f,*g;f=fopen("heavymetal.in","r");g=fopen("heavymetal.out","w");
	fscanf(f,"%ld",&n);for(i=1;i<=n;i++)fscanf(f,"%ld%ld",&a[i],&b[i]);
	for(i=n/2;i>=1;i--)hd(i,n);
	for(i=n;i>=1;i--){sh(1,i);hd(1,i-1);}
	max[1]=b[1]-a[1];
	for(i=2;i<=n;i++)
	{ if(b[i-1]<=a[i])max[i]=max[i-1]+b[i]-a[i];
	  else
	  { max[i]=max[i-1];
	    if(b[1]<=a[i])
	    { j=cauta(1,i-1);
	      if(max[j]+b[i]-a[i]>max[i])max[i]=max[j]+b[i]-a[i];
	    }
	  }
	}
	fprintf(g,"%ld\n",max[n]);
	fcloseall();
	return 0;
}
void hd(long int ic,long int nc)
{
	long int is,is1;
	is=2*ic;is1=2*ic+1;
	if(is>nc)return;
	if(is<nc)if(b[is1]>b[is])is=is1;
	if(b[is]>b[ic]){sh(is,ic);hd(is,nc);}
}
void sh(long int i1,long int i2)
{
	aux=a[i1];a[i1]=a[i2];a[i2]=aux;
	aux=b[i1];b[i1]=b[i2];b[i2]=aux;
}
long int cauta(long int st,long int dr)
{       long int mid;
	if(st==dr-1) return st;
	mid=(st+dr)/2;
	if(b[mid]>a[i]) return cauta(st,mid);
	return cauta(mid,dr);
}