#include <bits/stdc++.h>

using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
int n,dp[100005];
struct interval
{
    int st,dr;
};
interval v[100005];
int cmp(interval a, interval b)
{
    if(a.dr!=b.dr) return a.dr<b.dr;
    else return a.st<b.st;
}
int cb(int x, int dr)
{
    int st=1;
    int rez=0;
    int mij=0;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(v[mij].dr<=x)
        {
           rez=mij;
            st=mij+1;
        }
        else
        {
            dr=mij-1;
        }
    }
    return rez;
}
int main()
{
    fin>>n;
    for(int i=1;i<=n;i++)
    {
        fin>>v[i].st>>v[i].dr;
    }
    sort(v+1,v+n+1,cmp);

    for(int i=1;i<=n;i++)
    {
        int ind=cb(v[i].st,i-1);
        dp[i]=max(dp[i-1], dp[ind]+v[i].dr-v[i].st);
    }
    fout<<dp[n];
    return 0;
}