#include <fstream>
#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
int dp[200009], v[200009];
struct elem
{
    int left, lungime;
};
int n;
vector <elem> a[200009];
pair <int, int> x[100009];
int norm (int x)
{
    int st=1, dr=2*n, retine=0;
    while (st<=dr)
    {
        int mij=(st+dr)/2;
        if (v[mij]>=x)
        {
            retine=mij;
            dr=mij-1;
        }
        else st=mij+1;
    }
    return retine;
}
int main ()
{
    f >> n;
    for (int i=1; i<=n; i++)
    {
        f >> x[i].first >> x[i].second;
        v[2*i-1]=x[i].first;
        v[2*i]=x[i].second;
    }
    sort (v+1, v+2*n+1);
    for (int i=1; i<=n; i++)
    {
        int r=norm(x[i].second);
        a[r].push_back({norm(x[i].first), x[i].second-x[i].first});
    }
    for (int i=1; i<=2*n; i++)
    {
        dp[i]=dp[i-1];
        for (int j=0; j<a[i].size(); j++)
            dp[i]=max(dp[i], dp[a[i][j].left]+a[i][j].lungime);
    }
    g << dp[2*n];
}