#include <bits/stdc++.h>

using namespace std;

ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");

int n, best[100005], maxim;
struct intervalPuscarie // :)))
{
    int x, y;
}v[100005];

bool cmp(intervalPuscarie a, intervalPuscarie b)
{
    if (a.y == b.y)
        return a.x < b.x;
    return a.y < b.y;
}

int main()
{
    fin >> n;
    for (int i = 1; i <= n; ++i)
        fin >> v[i].x >> v[i].y, best[i] = v[i].y - v[i].x;
    sort(v + 1, v + n + 1, cmp);
    for (int i = 2; i <= n; ++i)
    {
        int maxx = 0;
        for (int j = i - 1; j >= 1; --j)
        {
            if (v[i].x >= v[j].y && best[i] + best[j] > maxx)
            {
                maxx = best[i] + best[j];
            }
        }
        if (maxx > 0)
            best[i] = maxx;
        maxim = max(maxim, best[i]);
    }
    fout << maxim;
    return 0;
}