#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Edge = pair<int, int>;
using Graph = vector<vector<Edge>>;
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define SORT(v) sort((v).begin(), (v).end())
#define RSORT(v) sort((v).rbegin(), (v).rend())
const ll MOD = 1000000007;
const ll nmax = 8;
const ll INF = 1e9;
bool graph[nmax][nmax];
vector<vector<ll>> dist = vector<vector<ll>>(nmax, vector<ll>(nmax, INF));
void warshall_floyd(ll n)
{
    for (size_t i = 0; i < n; i++)
    {
        for (size_t j = 0; j < n; j++)
        {
            for (size_t k = 0; k < n; k++)
            {
                dist[j][k] = min(dist[j][k], dist[j][i] + dist[i][k]);
            }
        }
    }
}

class UnionFind
{
public:
    vector<ll> Parent;

    UnionFind(ll N)
    {
        Parent = vector<ll>(N, -1);
    }
    ll find(ll A)
    {
        if (Parent[A] < 0)
            return A;
        return Parent[A] = find(Parent[A]);
    }

    ll size(ll A)
    {
        return -Parent[find(A)];
    }

    bool Union(ll A, ll B)
    {
        A = find(A);
        B = find(B);
        if (A == B)
        {
            return false;
        }
        if (size(A) < size(B))
            swap(A, B);

        Parent[A] += Parent[B];
        Parent[B] = A;

        return true;
    }
};

ll gcd(ll a, ll b)
{
    if (b == 0)
        return a;
    return gcd(b, a % b);
}

ll lcm(ll a, ll b)
{
    ll g = gcd(a, b);
    return a / g * b;
}

ll mulMod(ll a, ll b)
{
    return (((a % MOD) * (b % MOD)) % MOD);
}

ll powMod(ll a, ll p)
{
    if (p == 0)
    {
        return 1;
    }
    else if (p % 2 == 0)
    {
        ll half = powMod(a, p / 2);
        return mulMod(half, half);
    }
    else
    {
        return mulMod(powMod(a, p - 1), a);
    }
}

ll ceil(ll a, ll b)
{
    return (a + b - 1) / b;
}
bool opera(const pair<ll, ll> &student1, pair<ll, ll> &student2)
{
    if (student1.first == student2.first)
    {
        return student1.second > student2.second;
    }
    return student1.first < student2.first;
}
int main()
{
    long long N;
    scanf("%lld", &N);

    vector<pair<ll, ll>> p(N);
    vector<pair<ll, ll>> left(N);
    vector<pair<ll, ll>> right(N);
    for (int i = 0; i < N; i++)
    {

        ll l, r;
        cin >> l >> r;
        r++;
        left[i] = make_pair(l, r);
        right[i] = make_pair(r, l);
        p[i] = make_pair(l, r);
    }
    RSORT(left);
    SORT(right);

    auto most_left = left[0];
    auto most_right = right[0];

    ll ans_same = 0;
    ll ans_diff = 0;

    pair<ll, ll> longest = p[0];
    for (int i = 0; i < N; i++)
    {
        if (longest.second - longest.first < p[i].second - p[i].first)
        {
            longest = p[i];
        }
    }

    ans_same = max(0LL, most_right.first - most_left.first) + longest.second - longest.first;

    vector<pair<ll, ll>> ab(N);
    for (int i = 0; i < N; i++)
    {
        ab[i] = make_pair(max(p[i].second - most_left.first, 0LL), max(most_right.first - p[i].first, 0LL));
    }

    sort(ab.begin(), ab.end(), opera);
    ll w = INF;
    for (int i = 0; i < N; i++)
    {
        if (i)
        {
            ans_diff = max(ans_diff, w + ab[i].first);
        }

        w = min(w, ab[i].second);
    }

    cout << max(ans_same, ans_diff) << endl;
    return 0;
}


Measured memory_bytes: 6528