#include <fstream>
#include <algorithm>

using namespace std;

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

struct concerte
{
    int x,y;
} v[10001];
bool comp(concerte a, concerte b)
{
    return (a.y<b.y)||(a.y==b.y&&a.x<b.x);
}
long long n,i,j,smax,s[40000];

int main()
{
    f>>n;
    for(i=1; i<=n; i++)
    {
        f>>v[i].x>>v[i].y;
    }
    sort(v+1,v+n+1,comp);
    for(i=n; i>=1; i--)
    {
        s[i]=v[i].y-v[i].x;
        for(j=i+1; j<=n; j++)
        {
            if(v[i].y<=v[j].x&&s[j]+(v[i].y-v[i].x)>s[i])
            {
                s[i]=s[j]+(v[i].y-v[i].x);
            }
        }
    }
    for(i=1; i<=n; i++)
    {
        smax=max(s[i],smax);
    }
    g<<smax;

    return 0;
}