#include <iostream>
#include <stdio.h>
#include <algorithm>
using namespace std;

struct concert {int st, dr;};

const int NMAX = 100005;
concert v[NMAX];
int vmax[NMAX];

bool cmp(concert a, concert b) {
    return a.dr < b.dr;
}

int main() {

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

    int n, i, left, right, mid, r;

    scanf ("%d", &n);
    for (i = 1; i <= n; i++)
        scanf ("%d%d", &v[i].st, &v[i].dr);
    sort (v + 1, v + n + 1, cmp);

    for (i = 1; i <= n; i++) {
        left = 0;
        right = i - 1;
        while (left <= right) {
            mid = (left + right) / 2;
            if (v[mid].dr <= v[i].st) {
                r = mid;
                left = mid + 1;
            }
            else
                right = mid - 1;
        }
        vmax[i] = max(vmax[r] + v[i].dr - v[i].st, vmax[i - 1]);
    }

    printf ("%d", vmax[n]);

    return 0;
}