#include <iostream>
#include <fstream>
#include <set>
#include <algorithm>
#define DN 100005
#define mp make_pair
#define f first
#define s second
#define kind pair< pair<int,int> , int >
using namespace std;

int best[DN],normal[2*DN],n;
kind v[DN];
set<int> s;
set<int>::iterator it;


int caut_bin(int x)
{
    int left=1,right=n,mij,rez=0;
    while(left<=right)
    {
        mij=(left+right)/2;
        if( x <= v[mij].f.s)
        {
            rez=mij;
            right=mij-1;
        }
        else
            left=mij+1;
    }
    return rez;
}

void normalizare()
{
    int i=0;
    for(it=s.begin();it!=s.end();++it)
        normal[*it]=++i;
}

struct cmp
{
    bool operator()(const kind &a,const kind &b)const
    {
        if(a.f.s == b.f.s)
            return a.f.f < b.f.f;
            else
                return a.f.s < b.f.s ;
    }

};

int main()
{
    int tmax=0;
    ifstream f("heavymetal.in");
    ofstream g("heavymetal.out");
    f>>n;
    for(int i=1;i<=n;++i)
    {
        int x,y;
        f>>x>>y;
        s.insert(x);
        s.insert(y);
        v[i]=mp( mp(x,y) , y-x ) ;

    }
    normalizare();
    for(int i=1;i<=n;++i)
    {
        v[i].f.f=normal[v[i].f.f];
        v[i].f.s=normal[v[i].f.s];

        tmax=max(tmax,v[i].f.s);
    }

    sort(v+1,v+n+1,cmp());
   //  for(int i=1;i<=n;++i)
    //    cout<<v[i].f.f<<" "<<v[i].f.s<<endl;
    for(int i=1;i<=tmax;++i)
    {
        best[i]=best[i-1];
        int j=caut_bin(i)-1;
        while( v[++j].f.s == i && j<=n)
                best[i]= max ( best [i] , best [ v[j].f.f ] + v[j].s );
    }

    g<<best[tmax];

    return 0;
}