#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
int hi,lo,mijl,poz,i,sol[100001],n;
struct cub
{
    int st;
    int dr;
}v[100001];
int cmp(cub o, cub p)
{
    return o.dr<p.dr;
}
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i].st>>v[i].dr;
    sort(v+1,v+n+1,cmp);
    for(i=1;i<=n;i++)
    {
        sol[i]=sol[i-1];
        lo=1;
        hi=i-1;
        poz=0;
        while(lo<=hi)
        {
            mijl=lo+(hi-lo)/2;
            if(v[mijl].dr<=v[i].st)
            {
                lo=mijl+1;
                poz=mijl;
            }
            else
                hi=mijl-1;
        }
        sol[i]=max(sol[i],sol[poz]+v[i].dr-v[i].st);
    }
    fout<<sol[n];
    return 0;
}