#include <fstream>
#include <algorithm>

using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
struct kys{int x,y;}a[100001];
int compare (kys a,kys b)
{
    return a.y<b.y||a.y==b.y&&a.x<b.x;
}
int n,i,max1,s[100001],j;
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
    {
        fin>>a[i].x>>a[i].y;
    }
    sort(a+1,a+n+1,compare);
    for(i=1;i<=n-1;i++)
    {
        for(j=i+1;j<=n;j++)
        {
            if(a[i].y<=a[j].x&&s[j]<s[i]+a[i].y-a[i].x)s[j]=s[i]+a[i].y-a[i].x;
        }
    }
    for(i=1;i<=n;i++)
    {
        s[i]+=(a[i].y-a[i].x);
        if(s[i]>max1) max1=s[i];
    }
    fout<<max1;
    return 0;
}