#include<cstdio>
#include<algorithm>
using namespace std;
struct MATI
{
    int x,y;
};
MATI a[100005];
int d[100005];
bool cmp(MATI a,MATI b)
{
    return a.y<b.y;
}
int main()
{
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    int n,i,st,dr,med,last,maxim=0,q,z;
    scanf("%d",&n);
    for(i=1; i<=n; i++)
    {
        scanf("%d%d",&q,&z);
        a[i].x=q;
        a[i].y=z;
    }
    sort(a+1,a+n+1,cmp);
    for(i=1; i<=n; i++)
    {
        st=1;
        dr=i;
        while(st<=dr)
        {
            med=(st+dr)/2;
            if(a[med].y<=a[i].x)
            {
                st=med+1;
                last=med;
            }
            else
                dr=med-1;
        }
        d[i]=max(d[i-1],d[(st+dr)/2]+a[i].y-a[i].x);
        if(d[i]>maxim)
            maxim=d[i];
    }
    printf("%d\n",maxim);
    return 0;
}