#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
struct bongos
{
    int s,f;
}a[100005];
int n,i,st,dr,sum[100005],x;
int comp(bongos a,bongos b)
{
    return (a.f<b.f)||(a.f==b.f && a.s<b.s);
}
int main()
{
    f>>n;
    for(i=1;i<=n;i++)
    {
        f>>a[i].s>>a[i].f;
    }
    sort(a+1,a+n+1,comp);
    for(i=1;i<=n;i++)
    {
        st=1;
        dr=i;
        while(st<=dr)
        {
            int mij=(st+dr)/2;
            if(a[mij].f<=a[i].s)
            {
                st=mij+1;
                x=mij;
            }
            else
                dr=mij-1;
        }
       sum[i]=max(sum[i-1],sum[x]+a[i].f-a[i].s);
    }
    g<<sum[n];
    return 0;
}