#include <fstream>
#include <algorithm>
#include <vector>
using namespace std;
ifstream in("heavymetal.in");
ofstream out("heavymetal.out");
pair<int,int> a[100001];
int sol[100001],n,mx;
int main()
{
    in>>n;
    for(int i=1;i<=n;i++)
        in>>a[i].first>>a[i].second;
    sort(a+1,a+n+1);
    for(int i=1;i<=n;i++)
    {
        sol[i]=a[i].second-a[i].first;
        for(int j=i-1;j>=0;j--)
            if(a[j].second<=a[i].first)
            sol[i]=max(sol[i],sol[j]+a[i].second-a[i].first);
        mx=max(sol[i],mx);
    }
    out<<mx;
    return 0;
}