#include <fstream>
#include <algorithm>
using namespace std;
ifstream cin("heavymetal.in");
ofstream cout("heavymetal.out");
const int nmax=100000;
struct interval
{
    int st,dr;
};
struct solutie
{
    int last,scor;
};
bool cmp(interval a,interval b)
{
    if(a.dr==b.dr)
        return a.st>b.st;
    return a.dr<b.dr;
}
int n;
interval v[nmax+5];
solutie sol[nmax+5];
int main()
{
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        cin>>v[i].st>>v[i].dr;
    }
    sort(v+1,v+n+1,cmp);
    for(int i=1;i<=n;i++)
    {
        /**


        **/
        int r=0,pas=1<<16;
        while(pas)
        {
            if(r+pas<=i-1 and sol[r+pas].last<=v[i].st)
            {
                r+=pas;
            }
            pas/=2;
        }
        sol[i].last=v[i].dr;
        sol[i].scor=sol[r].scor+v[i].dr-v[i].st;
    }
    /**for(int i=1;i<=n;i++)
    {
        cout<<sol[i].last<<" "<<sol[i].scor<<"\n";
    }
    cout<<"\n\n\n";**/
    int ma=0;
    for(int i=1;i<=n;i++)
        ma=max(ma,sol[i].scor);
    cout<<ma;
    return 0;
}