#include <bits/stdc++.h>
using namespace std;
#define REP(i, n) FOR(i, 0, n)
#define FOR(i, s, n) for (int i = (s), i##_len = (n); i < i##_len; ++i)
#define ALL(obj) (obj).begin(), (obj).end()
#define ALLR(obj) (obj).rbegin(), (obj).rend()

#define isvisiblechar(c) (0x21 <= (c) && (c) <= 0x7E)
#define cin scanner
#define cout printer
#define endl '\n'
namespace {
class MaiScanner {
  public:
    template <typename T> void input_integer(T &var) {
        var = 0;
        char ch = getchar_unlocked(), sign = 1;
        while (ch < '0' || ch > '9') {
            if (ch == '-')
                sign = -1;
            ch = getchar_unlocked();
        }
        while (ch >= '0' && ch <= '9')
            var = (var << 3) + (var << 1) + ch - '0', ch = getchar_unlocked();
        var = var * sign;
    }
    inline MaiScanner &operator>>(int &var) {
        input_integer<int>(var);
        return *this;
    }
    inline MaiScanner &operator>>(long long &var) {
        input_integer<long long>(var);
        return *this;
    }
    inline MaiScanner &operator>>(string &var) {
        char cc = getchar_unlocked();
        for (; !isvisiblechar(cc); cc = getchar_unlocked())
            ;
        for (; isvisiblechar(cc); cc = getchar_unlocked())
            var.push_back(cc);
        return *this;
    }
    template <typename IT> void in(IT begin, IT end) {
        for (auto it = begin; it != end; ++it)
            *this >> *it;
    }
};
class MaiPrinter {
  public:
    template <typename T> void output_integer(T var) {
        if (var == 0) {
            putchar_unlocked('0');
            return;
        }
        if (var < 0)
            putchar_unlocked('-'), var = -var;
        char stack[32];
        int stack_p = 0;
        while (var)
            stack[stack_p++] = '0' + (var % 10), var /= 10;
        while (stack_p)
            putchar_unlocked(stack[--stack_p]);
    }
    inline MaiPrinter &operator<<(char c) {
        putchar_unlocked(c);
        return *this;
    }
    inline MaiPrinter &operator<<(int var) {
        output_integer<int>(var);
        return *this;
    }
    inline MaiPrinter &operator<<(long long var) {
        output_integer<long long>(var);
        return *this;
    }
    inline MaiPrinter &operator<<(char *str_p) {
        while (*str_p)
            putchar_unlocked(*(str_p++));
        return *this;
    }
    inline MaiPrinter &operator<<(const string &str) {
        const char *p = str.c_str();
        const char *l = p + str.size();
        while (p < l)
            putchar_unlocked(*p++);
        return *this;
    }
    template <typename IT> void join(IT begin, IT end, char sep = ' ') {
        for (bool b = 0; begin != end; ++begin, b = 1)
            b ? *this << sep << *begin : *this << *begin;
    }
};
} // namespace
MaiScanner scanner;
MaiPrinter printer;

int main() {
    int n;
    cin >> n;
    vector<int> a(n), b(n);
    REP(i, n) cin >> a[i] >> b[i];
    int maxx = *max_element(ALL(a));
    int minn = *min_element(ALL(b));
    int ans = 0;
    vector<pair<int, int>> p(n);
    for (int i = 0; i < n; ++i)
        p[i] = {minn - a[i] + 1, b[i] - maxx + 1};
    sort(ALL(p));
    // for (auto& e: p)
    //  cout << e.first << ' ' << e.second << '\n';
    int t = INT_MAX;
    for (int i = 0; i < n - 1; ++i) {
        t = min(t, p[i].second);
        ans = max(ans, p[i + 1].first + t);
    }
    t = max(0, minn - maxx + 1);
    for (int i = 0; i < n; ++i) {
        int cur = b[i] - a[i] + t + 1;
        ans = max(ans, cur);
    }
    cout << ans << '\n';
}


Measured memory_bytes: 1792