#include <bits/stdc++.h>
#define nmax 100005

using namespace std;

struct numere
{
    int st;
    int dr;
} num[nmax];

int n;
int dinamica[nmax];

bool cmp(numere a, numere b)
{
    if(a.dr==b.dr)
        return a.st<b.st;
    return a.dr<b.dr;
}
int find_k(int s, int d, int current)
{
    int med;
    int raspuns;
    int maxim=0;
    while(s<=d)
    {
        med=(s+d)/2;
        if(num[med].dr>num[current].st)
            d=med-1;
        else
        {
            s=med+1;
            if(dinamica[med]>maxim)
                raspuns=med;
        }
    }
    return raspuns;
}

void citire()
{
    scanf("%d", &n);
    for(int i=1; i<=n; i++)
    {
        int s, d;
        scanf("%d%d", &s, &d);
        num[i].st=s;
        num[i].dr=d;
    }
}
void rezolvare()
{
    sort(num+1, num+n+1, cmp);
    dinamica[1]=num[1].dr-num[1].st;
    for(int i=2; i<=n; i++)
    {
        int k;
        k=find_k(1, n, i);
        dinamica[i]=max(dinamica[i-1], num[i].dr-num[i].st+dinamica[k]);
    }
}
void afisare()
{
    printf("%d\n", dinamica[n]);
}

int main()
{
    freopen("heavymetal.in", "r", stdin);
    freopen("heavymetal.out", "w", stdout);

    citire();
    rezolvare();
    afisare();

    return 0;
}