#include<cstdio>
#include<cstring>
int b[5001],e[5001],f[5001],ans;
int max(int x,int y)
{
	if (x>y) return x;
	else return y;
}
void qsort(int l,int r)
{
	int i,j,m,p;
	i=l;j=r;
	m=b[(l+r)/2];
	do
	{
	 while (b[i]<m) i++;
	 while (b[j]>m) j--;
	 if (i<=j)
	 {
	  p=b[i];b[i]=b[j];b[j]=p;
	  p=e[i];e[i]=e[j];e[j]=p;
	  i++;j--;
	 }
	}
	while (i<=j);
	if (i<r) qsort(i,r);
	if (l<j) qsort(l,j);
}
int main()
{
	int n,i,j;
	scanf("%d",&n);
	for(i=1;i<=n;i++)
	  scanf("%d%d",&b[i],&e[i]);
	qsort(1,n);
	memset(f,-127,sizeof(f));
	for(i=1;i<=n;i++)
	  f[i]=e[i]-b[i];
	for(i=2;i<=n;i++)
	  for(j=1;j<=i-1;j++)
	    if (b[i]>=e[j]) f[i]=max(f[i],f[j]+e[i]-b[i]);
	ans=0;
	for(i=1;i<=n;i++)
	  if (f[i]>ans) ans=f[i];
	printf("%d",ans);
}