#include<stdio.h> 
#include<stdlib.h>
#include<algorithm>
#define N 100010  
using namespace std;
struct interval{  
    int a,b;  
};
interval v[N];
struct timp{
	int cost,ora;
};
timp best[N];
int compar(const void*x,const void*y){  
	interval *aa=(interval *)x,*bb=(interval *)y;
	if (aa->b<bb->b)  
		return -1;  
	if (aa->b>bb->b)  
		return 1;  
	if (aa->a>bb->a)  
		return 1;  
	if (aa->a<bb->a)  
		return -1;  
	return 0;  
}  

int f_comp(interval x,interval y){
	return x.a<y.a;
}
int caut(int p,int u,int x,int n){
	int m;
	/*
	while(p<=u){
		m=(p+u)/2;
		if (best[m].ora<=x && best[m+1].ora>x || best[m].ora<=x && m==n)
			return m;
		else 
			if (best[m].ora<=x && best[m+1].ora<=x)
				p=m-1;
			else
				u=m+1;
	}
	return 0;
	*/
	while(p<u){
		m=(p+u)/2;
		if(x<=best[m].ora)
			u=m;
		else
			p=m+1;
	}
	if(best[p].ora>x)
		--p;
	return p;
}
int main(){  
	int n,i,s=0,t,j,x,m=0;
	int poz,p,u,b[N]={0};
	freopen("heavymetal.in","r",stdin);  
	freopen("heavymetal.out","w",stdout);  
	scanf("%d",&n);  
	for (i=0;i<n;++i){  
		scanf("%d%d",&v[i].a,&v[i].b);  
	}
	sort(v,v+n,f_comp);
	best[m].cost=v[0].b-v[0].a;
	best[m++].ora=v[0].b;
	for(i=1;i<n;++i){
		poz=caut(0,m-1,v[i].a,m);//best[poz].ora va fi cea mai mare ora inainte de v[i].a
		if(v[i].b==best[m-1].ora){
			if(best[poz].cost+v[i].b-v[i].a>best[m-1].cost)
				best[m-1].cost=best[poz].cost+v[i].b-v[i].a;
		}
		else
			if(best[poz].cost+v[i].b-v[i].a>best[m-1].cost){
				best[m].cost=best[poz].cost+v[i].b-v[i].a;
				best[m++].ora=v[i].b;
			}
			/*
			else{//e cam in plus...
				best[m].cost=best[m-1].cost;
				best[m++].ora=v[i].b;
			}
			*/
	}
	printf("%d\n",best[m-1].cost);
	return 0;  
}