#include<stdio.h>
#include<stdlib.h>
struct interval
{
	int a,b;
};
interval v[100000];
int compar(const void *p,const void *q)
{
	interval *pp=(interval*)p,*qq=(interval*)q;
	interval u=*pp,w=*qq;
	if(u.a<w.a)
		return -1;
	if(u.a>w.a)
		return 1;
	return w.b-u.b;
}
int main()
{
	freopen("heavymetal.in","r",stdin);
	freopen("heavymetal.out","w",stdout);
	int n,i,x=1;
	long long s=0;
	scanf("%d",&n);
	for(i=0; i<n; i++)
	{
		scanf("%d%d",&v[i].a,&v[i].b);
	}
	qsort(v,n,sizeof(v[0]),compar);
	for(i=0; i<n; i++)
	{
		//printf("%d %d\n",v[i].a,v[i].b);
		if(v[i].a>=x)
		{
			s+=v[i].b-v[i].a;
			x=v[i].b;
		}
	}
	printf("%lld\n",s);
	return 0;
}