#include<stdio.h>
#include<stdlib.h>
struct STRUCT {int a,b;};
STRUCT v[100005];
int comp(const void *a,const void *b)
{
	STRUCT *pa,*pb;
	pa=(STRUCT*)a;pb=(STRUCT*)b;
	if(pa->a==pb->a)
		return pb->b-pa->b;
	return pa->a-pb->a;
}
int main()
{
	freopen("heavymetal.in","r",stdin);
	freopen("heavymetal.out","w",stdout);
	int dr=0,n,i,s=0;
	scanf("%d",&n);
	for(i=1;i<=n;i++)
		scanf("%d%d",&v[i].a,&v[i].b);
	qsort(v+1,n,sizeof(v[0]),comp);
	for(i=1;i<=n;i++)
		if(v[i].a>=dr)
		{
			dr=v[i].b;
			s=s+v[i].b-v[i].a;
		}
	printf("%d\n",s);
	return 0;
}