#include <iostream>
#include <fstream>
#include <algorithm>
#define NMAX 100005
#define pii pair <int, int>
using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");

int n;
long long dp[NMAX];
pii a[NMAX];

bool cmp (pii x, pii y)
{
    return x.second < y.second;
}

int main()
{
    fin >> n;
    for (int i = 1; i <= n; i++)
        fin >> a[i].first >> a[i].second;
    sort (a + 1, a + n + 1, cmp);
    for (int i = 1; i <= n; i++)
    {
        int st = 0, dr = i;
        int nxt = a[i].first;
        while (st < dr)
        {
            int mij = (st + dr + 1) / 2;
            if (nxt >= a[mij].second)
                st = mij;
            else dr = mij - 1;
        }
        dp[i] = max(dp[i - 1], dp[st] + a[i].second - a[i].first);
    }
    fout << dp[n] << "\n";
    return 0;
}