#include <deque>
#include <algorithm>
#include <fstream>

using namespace std;

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

int n;
pair < int, int > v[100005];
int sol[15];

bool cmp(pair < int, int > a, pair < int, int > b)
{
    return (a.second<b.second?true:(a.second==b.second?a.first<b.first:false));
}

int caut_bin(int k)
{
    int i = 0, pas = 1 << 16;
    while (pas != 0) {
        if (i + pas <= n && k <= v[i + pas].first) i+=pas;
        pas /= 2;
    }
    return i;
}

int main()
{
    fin>>n;
    for (int i = 1; i <= n; i++) {
        fin>>v[i].first>>v[i].second;
    }
    sort(v + 1, v + n + 1, cmp);
    int j, s;
    sol[1] = v[1].second - v[1].first;
    for (int i = 2; i <= n; i++) {
        j = caut_bin(v[i].second);
        s = v[j].second - v[j].first + v[i].second - v[i].first;
        sol[i] = max(s, sol[i - 1]);
    }
    fout<<sol[n];
}