#include<stdio.h>
//#include<algorithm>
#define NMAX 101001
//using namespace std;
long p,i,y[NMAX],poz,in,sf,a,j,k,l,n,m,q;
struct kkt
{
	long X,Y;
};
kkt x[NMAX],aux;
/*int cmpf(const kkt a,const kkt b)
{
	return a.Y>b.Y;
} */
long mx(long a,long b)
{
	if (a>b) return a;
	return b;
}
int main()
{
	freopen("heavymetal.in","r",stdin);
	freopen("heavymetal.out","w",stdout);
	scanf("%ld",&n);
	for (i=1;i<=n;i++)
		scanf("%ld%ld",&x[i].X,&x[i].Y);
	a=1;
	while (a)
	{
		a=0;
		for (i=1;i<n;i++)
			if (x[i].Y>x[i+1].Y)
			{
				aux=x[i];
				x[i]=x[i+1];
				x[i+1]=aux;
				a=1;
			}
	}
//	sort(x+1,x+n+1,cmpf);
	for (i=1;i<=n;i++)
	{
		y[x[i].Y]=y[x[i].Y-1];
		for (j=1;j<=n;j++)
			if (x[j].Y==x[i].Y)
				y[x[i].Y]+=mx(y[x[i].Y],y[x[j].X]+(x[j].Y-x[j].X));
		if (y[x[i].Y]>p)
			p=y[x[i].Y];
	}
	printf("%ld\n",p);

	return 0;
}