#include <bits/stdc++.h>
using namespace std;
 
#define int long long
#define REP(i, l, r) for (int i=(l); i<(r); ++i)
#define RREP(i, r, l) for (int i=(r); i>(l); --i)
#define CASET int _T; cin >> _T; REP(caset, 0, _T)
#define print(x) cout << to_string(x) << '\n'
#define vi vector<int>
#define vb vector<bool>
#define vs vector<string>
#define vvi vector<vi>
#define vvb vector<vb>
#define pii pair<int,int>
#define t3i tuple<int,int,int>
#define mii map<int,int>
#define vpii vector<pii>
#define vt3i vector<t3i>
#define sq(x) (x)*(x)
#define inv(x) powa(x, MOD-2)
 
long long INF = 1LL<<60;
long long MOD = 1e9+7;
 
string to_string(char &c) {string x(1, c); return x;}
string to_string(const char s[]) {return (string)s;}
string to_string(string &s) {return s;}
string to_string(vb &v) {string res; for (const bool &x : v) res += to_string(x) + ' '; return res;}
template <class C> string to_string(C &v) {string res; for (auto &x : v) res += to_string(x) + ' '; return res;}
template <typename A, typename B> istream &operator>>(istream &is, pair<A, B> &pr) {is >> pr.first >> pr.second; return is;}
template <typename A> istream &operator>>(istream &is, vector<A> &v) {for (auto &x : v) is >> x; return is;}
ostream &operator<<(ostream &os, char &c) {os << (char)c; return os;}
ostream &operator<<(ostream &os, const char s[]) {os << (string)s; return os;}
ostream &operator<<(ostream &os, string &s) {for (char &c : s) os << (char)c; return os;}
template <typename A, typename B> ostream &operator<<(ostream &os, pair<A, B> pr) {os << '(' << pr.first << ", " << pr.second << ')'; return os;}
ostream &operator<<(ostream &os, vb &v) {
    bool first = true;
    os << '[';
    for (const bool &x : v) {
        if (!first) os << ", ";
        first = false;
        os << x;
    }
    os << ']';
    return os;
}
template <class C> ostream &operator<<(ostream &os, C &v) {
    bool first = true;
    os << '[';
    for (auto &x : v) {
        if (!first) os << ", ";
        first = false;
        os << x;
    }
    os << ']';
    return os;
}
string bin_string(int x) {
    const int d = 32;
    string res(d, ' ');
    REP(i, 0, d) res[d-1-i] = '0'+(x>>i & 1LL);
    return res;
}
int powa(int base, int exp) {
    int res = 1;
    while (exp) {
        if (exp&1) res = res*base % MOD;
        base = base*base % MOD;
        exp >>= 1;
    }
    return res;
}

main() {
    ios::sync_with_stdio(0), cin.tie(0);
    
    int n;
    cin >> n;
    vpii segs(n);
    multiset<int> lefts, rights;
    REP(i, 0, n) {
        cin >> segs[i].first >> segs[i].second;
        lefts.insert(segs[i].first);
        rights.insert(segs[i].second);
    }
    sort(segs.begin(), segs.end());

    int res = 0;
    REP(i, 0, n) {
        lefts.erase(lefts.find(segs[i].first));
        rights.erase(rights.find(segs[i].second));
        res = max(res, segs[i].second-segs[i].first+1 + max(0LL, *rights.begin() - *lefts.rbegin() + 1));
        lefts.insert(segs[i].first);
        rights.insert(segs[i].second);
    }
    
    vpii segs0 = segs;
    segs = {segs.back()};
    RREP(i, n-2, -1) {
        if (segs0[i].second < segs.back().second) segs.push_back(segs0[i]);
    }
    reverse(segs.begin(), segs.end());
    
    n = segs.size();
    REP(i, 1, n) {
        res = max(res, segs[0].second-segs[i-1].first+1 + segs[i].second-segs.back().first+1);
    }
    print(res);
}

Measured memory_bytes: 12800