#include <fstream>
#include <algorithm>

using namespace std;

ifstream f("heavymetal.in");
ofstream g("heavymetal.out");

struct hh{
    int x,y;
};
hh v[100001];
int n,i,s=0,t=1,a[100001];

int cmp(hh a,hh b)
{
    if(a.y>b.y)
        return false;
    if(a.x>b.x && a.y==b.y)
        return false;
    return true;
}

int main()
{
    f>>n;
    for(i=1;i<=n;i++)
        f>>v[i].x>>v[i].y;
    sort(v+1,v+n+1,cmp);
    for(i=1;i<=v[n].y;i++)
    {
        a[i]=a[i-1];
        while(i==v[t].y)
        {
            a[i]=max(a[i],v[t].y-v[t].x+a[v[t].x]);
            t++;
        }
    }
    g<<a[v[n].y];
    return 0;
}