#include <bits/stdc++.h>
using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
int n, best[100005], maxx[100005], maxim_local, maxim;
struct Interval
{
    int x, y;
}v[100005];
bool cmp(Interval a, Interval b)
{
    if (a.y == b.y)
        return a.x < b.x;
    return a.y < b.y;
}
int cautbin(int i)
{
    int st = 1, dr = i - 1, sol = -1;
    while (st <= dr)
    {
        int mid = (st + dr) / 2;
        if (v[mid].y <= v[i].x)
        {
            sol = mid;
            st = mid + 1;
        }
        else
        {
            dr = mid - 1;
        }
    }
    return sol;
}
int main()
{
    fin >> n;
    for (int i = 1; i <= n; ++i)
        fin >> v[i].x >> v[i].y;
    sort(v + 1, v + n + 1, cmp);
    for (int i = 1; i <= n; ++i)
        best[i] = v[i].y - v[i].x;
    maxx[1] = best[1];
    for (int i = 2; i <= n; ++i)
    {
        int sol = cautbin(i);
        maxim_local = 0;
        if (sol > 0)
            maxim_local = maxx[sol];
        if (maxim_local > 0) best[i] = best[i] + maxim_local;
        maxim = max(maxim, best[i]);
        maxx[i] = max(maxx[i - 1], best[i]);
    }
    fout << maxim;
}