#include <bits/stdc++.h>
#define INF (1 << 30)
using namespace std;

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

int n, best[100005], maxim, arb[200005];
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 cautbin1(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;
            dr = mid - 1;
        }
        else
        {
            st = mid + 1;
        }
    }
    return sol;
}

int cautbin2(int i)
{
    int st = 1, dr = i - 1, sol = -2;
    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;
}

void build(int st, int dr, int nod)
{
    if (st > dr) return;
    if (st == dr)
    {
        arb[nod] = best[st];
        return;
    }
    int mid = (st + dr) / 2;
    build(st, mid, nod * 2);
    build(mid + 1, dr, nod * 2 + 1);
    arb[nod] = max(arb[nod * 2], arb[nod * 2 + 1]);

}

void Update(int st, int dr, int poz, int val, int nod)
{
    if (st > dr) return;
    if (poz < st || poz > dr)
    {
        return;
    }
    if (st == dr)
    {
        arb[nod] = val;
        return;
    }
    int mid = (st + dr) / 2;
    Update(st, mid, poz, val, nod * 2);
    Update(mid + 1, dr, poz, val, nod * 2 + 1);
    arb[nod] = max(arb[nod * 2], arb[nod * 2 + 1]);
}

int query(int st, int dr, int a, int b, int nod)
{
    if (st > b || dr < a) return -INF;
    if (st >= a && dr <= b) return arb[nod];
    int mid = (st + dr) / 2;
    return max(query(st, mid, a, b, nod * 2), query(mid + 1, dr, a, b, nod * 2 + 1));
}

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;
    }
    build(1, n, 1);
    for (int i = 2; i <= n; ++i)
    {
        int maxx = best[i];
        int a = cautbin1(i);
        int b = cautbin2(i);
        if (a != -1)
        {
            maxx = query(1, n, a, b, 1);
            best[i] += maxx;
            Update(1, n, i, best[i], 1);
        }
        maxim = max(maxim, best[i]);
    }
    fout << maxim;
    return 0;
}