#include<fstream>
#include<algorithm>
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
struct cell
{
    int st, dr;
}v[100002];
int n,dp[100002];
bool cmp(cell a,cell b)
{
    return a.dr<b.dr;
}
int main()
{
    f>>n;
    for(int i=1;i<=n;i++)
      f>>v[i].st>>v[i].dr;
    sort(v+1,v+n+1,cmp);
    for(int i=1;i<=n;i++)
    {
        int st=1;
        int dr=i-1;
        while(st<=dr)
        {
            int mij=(st+dr)/2;
            if(v[mij].dr<=v[i].st)
              st=mij+1;
            else
              dr=mij-1;
        }
        dp[i]=max(dp[i-1],dp[dr]+(v[i].dr-v[i].st));
    }
    g<<dp[n];
    return 0;
}