#include <fstream>
#include <algorithm>
using namespace std;

ifstream cin("heavymetal.in");
ofstream cout("heavymetal.out");

const int Nmax = 1e5 + 5;

struct interval
{
    int st, dr;
}v[Nmax];
bool cmp(interval a, interval b)
{
    if (a.dr != b.dr)
        return a.dr < b.dr;
    return a.st < b.st;
}
long long dp[Nmax];

int cb(int x, int i)
{
    int st = 1, dr = i, ans = 0;
    while (st <= dr)
    {
        int mid = (st + dr) / 2;
        if (v[mid].dr <= x)
        {
            ans = mid;
            st = mid + 1;
        }
        else
            dr = mid - 1;
    }
    return ans;
}

signed main()
{
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> v[i].st >> v[i].dr;
    sort(v + 1, v + n + 1, cmp);
    for (int i = 1; i <= n; i++)
    {
        int j = cb(v[i].st, i - 1);
        dp[i] = max((long long) dp[i - 1], (long long)dp[j] + v[i].dr - v[i].st);
    }
    cout << dp[n];
}