#include <stdio.h>
int a[1001],b[1001];
int n;
long max;
int main ()
{
	freopen ("heavymetal.in","r",stdin);
	freopen ("heavymetal.out","w",stdout);
	int i,j;
    long s;
	scanf ("%d",&n);
	for (i=1; i<=n; ++i)
	    scanf ("%d%d",&a[i],&b[i]);
    for (i=1; i<n; ++i)
    {
        s=b[i]-a[i];
        for (j=i+1; j<=n; ++j)
            if (b[i]<=a[j] || b[j]<=a[i])
			   s+=b[j]-a[j];
        if (s>max)
           max=s;
    }
    printf ("%ld",max);
    return 0;
}