#include <fstream>
#include <algorithm>
using namespace std;
struct punct
{
    int x,y;
}a[100005];
int n,i,j,v[100005],mx,mx1;
int compar(punct a,punct b)
{
    return ((a.y<b.y)||(a.y==b.y&&a.x<b.x));
}
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
int main()
{
    f>>n;
    for(i=1;i<=n;i++)
    {
        f>>a[i].x>>a[i].y;
    }
    sort(a+1,a+n+1,compar);
    j=1;
    for(i=1;i<=a[n].y;i++)
    {
        v[i]=v[i-1];
        while(a[j].y==i)
        {
            v[i]=max(v[i],v[a[j].x]+a[j].y-a[j].x);
            j++;
        }
    }
    g<<v[a[n].y];
    return 0;
}