#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
struct ceva
{
    int x,y,d;
} v[100001];
int comp(ceva A, ceva B)
{
    if(A.x==B.x) return A.y<B.y;
    else return A.x<B.x;
}
int Dmax;
int main()
{
    int n,i,dmax,j;
    f>>n;
    for(i=1;i<=n;i++)
        {f>>v[i].x>>v[i].y;
         v[i].d=v[i].y-v[i].x;}
    sort(v+1,v+n+1,comp);
    for(i=n-1;i>=1;i--)
    {
        dmax=0;
        for(j=i+1;j<=n;j++)
        {
            if(v[j].x>=v[i].y) if(v[j].d>dmax)dmax=v[j].d;

        }
        v[i].d+=dmax;
        if(v[i].d>Dmax)Dmax=v[i].d;
    }
    g<<Dmax;
    return 0;
}