#include<stdio.h>
#include<algorithm>
#define LMAX 100100
#define max(a,b) (a>b ? a : b)

using namespace std;

struct pozdy
{
	int x,y;
} a[LMAX];

int c[LMAX];

inline bool cmp(pozdy x,pozdy y)
{
	return x.y<y.y;
}

int cauta(int st,int dr,int val)
{
	int m,last=-1;
	while(st<=dr)
	{
		m=(st+dr)/2;
		if(a[m].y<=val)
			last=m,st=m+1;
		else
			dr=m-1;
	}
return last;	
}

int main()
{
	int i,n,poz;
	
	freopen("heavymetal.in","r",stdin);
	freopen("heavymetal.out","w",stdout);
	
	scanf("%d",&n);
	for(i=1;i<=n;i++)
		scanf("%d%d",&a[i].x,&a[i].y);
	sort(a+1,a+n+1,cmp);
	for(i=1;i<=n;i++)
	{
		poz=cauta(1,i-1,a[i].x); //cauta si vei gasi :)
		c[i]=c[i-1];
		if(poz==-1)
			c[i]=max(c[i],a[i].y-a[i].x);
		else
			c[i]=max(c[i],c[poz]+a[i].y-a[i].x);
		
	}
	printf("%d",c[n]);
}