#include<stdio.h>
long a[100001];
long b[100001];
long t[100001];
long max (long x , long y)
{
	if (x>y)
		return x;
	return y;
}

long part(long st , long dr)
{
	long p,m,i,j,aux;
	i=st-1;
	j=dr+1;
	m=(st+dr)/2;
	p=b[m];
	while (1)
	{
		do {++i;}while (b[i]<p);
		do {--j;}while (b[j]>p);
		if (i<j)
		{
			aux=b[i];
			b[i]=b[j];
			b[j]=aux;
			aux=a[i];
			a[i]=a[j];
			a[j]=aux;
		}
		else
			return j;
		
	}
}

void quick(long st , long dr)
{
	long sp;
	if (st<dr)
	{
		sp=part(st,dr);
		quick(st,sp);
		quick(sp+1,dr);
	}
}

int main()
{
	long n,i,j,u=0;
	
	freopen("heavymetal.in","r",stdin);
	freopen("heavymetal.out","w",stdout);
	
	scanf("%ld",&n);
	for (i=1;i<=n;i++)
		scanf("%ld%ld",&a[i],&b[i]);
	quick(1,n);
	for (i=1;i<=b[n];i++)
	{
		t[i]=t[i-1];
		for (j=1;j<=n;j++)
		{
			if (b[j]==i)
			{
				u=max(t[i],t[a[j]]+b[j]-a[j]);
				t[i]=u;
			}
			else
			{
				if (b[j]>i)
					break;
			}
		}
	}
	printf("%ld\n",t[b[n]]);
	return 0;
}