#include "bits/stdc++.h"
using namespace std;

using ll = long long;
const int INF = 1e9 + 7;
#define all(x) x.begin(), x.end()
#define pb push_back
#define cmax(x, y) (x = max(x, y))
#define cmin(x, y) (x = min(x, y))

#ifdef LOCAL
#include "debug.cpp"
#else
#define debug(x...)
#endif

template<const int &MOD>
struct _m_int {
    int val;
 
    _m_int(int64_t v = 0) {
        if (v < 0) v = v % MOD + MOD;
        if (v >= MOD) v %= MOD;
        val = int(v);
    }
 
    _m_int(uint64_t v) {
        if (v >= MOD) v %= MOD;
        val = int(v);
    }
 
    _m_int(int v) : _m_int(int64_t(v)) {}
    _m_int(unsigned v) : _m_int(uint64_t(v)) {}
 
    explicit operator int() const { return val; }
    explicit operator unsigned() const { return val; }
    explicit operator int64_t() const { return val; }
    explicit operator uint64_t() const { return val; }
    explicit operator double() const { return val; }
    explicit operator long double() const { return val; }
 
    _m_int& operator+=(const _m_int &other) {
        val -= MOD - other.val;
        if (val < 0) val += MOD;
        return *this;
    }
 
    _m_int& operator-=(const _m_int &other) {
        val -= other.val;
        if (val < 0) val += MOD;
        return *this;
    }
 
    static unsigned fast_mod(uint64_t x, unsigned m = MOD) {
#if !defined(_WIN32) || defined(_WIN64)
        return unsigned(x % m);
#endif
        // Optimized mod for Codeforces 32-bit machines.
        // x must be less than 2^32 * m for this to work, so that x / m fits in an unsigned 32-bit int.
        unsigned x_high = unsigned(x >> 32), x_low = unsigned(x);
        unsigned quot, rem;
        asm("divl %4\n"
            : "=a" (quot), "=d" (rem)
            : "d" (x_high), "a" (x_low), "r" (m));
        return rem;
    }
 
    _m_int& operator*=(const _m_int &other) {
        val = fast_mod(uint64_t(val) * other.val);
        return *this;
    }
 
    _m_int& operator/=(const _m_int &other) {
        return *this *= other.inv();
    }
 
    friend _m_int operator+(const _m_int &a, const _m_int &b) { return _m_int(a) += b; }
    friend _m_int operator-(const _m_int &a, const _m_int &b) { return _m_int(a) -= b; }
    friend _m_int operator*(const _m_int &a, const _m_int &b) { return _m_int(a) *= b; }
    friend _m_int operator/(const _m_int &a, const _m_int &b) { return _m_int(a) /= b; }
 
    _m_int& operator++() {
        val = val == MOD - 1 ? 0 : val + 1;
        return *this;
    }
 
    _m_int& operator--() {
        val = val == 0 ? MOD - 1 : val - 1;
        return *this;
    }
 
    _m_int operator++(int) { _m_int before = *this; ++*this; return before; }
    _m_int operator--(int) { _m_int before = *this; --*this; return before; }
 
    _m_int operator-() const {
        return val == 0 ? 0 : MOD - val;
    }
 
    friend bool operator==(const _m_int &a, const _m_int &b) { return a.val == b.val; }
    friend bool operator!=(const _m_int &a, const _m_int &b) { return a.val != b.val; }
    friend bool operator<(const _m_int &a, const _m_int &b) { return a.val < b.val; }
    friend bool operator>(const _m_int &a, const _m_int &b) { return a.val > b.val; }
    friend bool operator<=(const _m_int &a, const _m_int &b) { return a.val <= b.val; }
    friend bool operator>=(const _m_int &a, const _m_int &b) { return a.val >= b.val; }
 
    static const int SAVE_INV = int(1e6) + 5;
    static _m_int save_inv[SAVE_INV];
 
    static void prepare_inv() {
        // Ensures that MOD is prime, which is necessary for the inverse algorithm below.
        for (int64_t p = 2; p * p <= MOD; p += p % 2 + 1)
            assert(MOD % p != 0);
 
        save_inv[0] = 0;
        save_inv[1] = 1;
 
        for (int i = 2; i < SAVE_INV; i++)
            save_inv[i] = save_inv[MOD % i] * (MOD - MOD / i);
    }
 
    _m_int inv() const {
        if (save_inv[1] == 0)
            prepare_inv();
 
        if (val < SAVE_INV)
            return save_inv[val];
 
        _m_int product = 1;
        int v = val;
 
        do {
            product *= MOD - MOD / v;
            v = MOD % v;
        } while (v >= SAVE_INV);
 
        return product * save_inv[v];
    }
 
    _m_int pow(int64_t p) const {
        if (p < 0)
            return inv().pow(-p);
 
        _m_int a = *this, result = 1;
 
        while (p > 0) {
            if (p & 1)
                result *= a;
 
            p >>= 1;
 
            if (p > 0)
                a *= a;
        }
 
        return result;
    }
 
    friend ostream& operator<<(ostream &os, const _m_int &m) { return os << m.val; }
    friend istream& operator>>(istream &is, _m_int &m) {
        int64_t v;
        is >> v;
        m = _m_int(v);
        return is;
    }
};
 
template<const int &MOD> _m_int<MOD> _m_int<MOD>::save_inv[_m_int<MOD>::SAVE_INV];
 
const int MOD = 1000000007;
using mint = _m_int<MOD>;

const int MAXN = 5e5;
mint factorial[MAXN + 5];
int ile[MAXN + 5], height[2 * MAXN + 5];

mint newtwon(int a, int b) {
    if (b > a) return 0;
    return factorial[a] / (factorial[b] * factorial[a - b]);
}

void solve() {
    int n;
    cin >> n;
    vector <pair <int, int>> v(n + 1);
    for (int i = n; i >= 1; i--) {
        cin >> v[i].first >> v[i].second;
    }

    vector <set <int>> st(n + 1);
    for (int i = 1; i <= n; i++) {
        int l = -1, r = -1;
        for (int j = i + 1; j <= n; j++) {
            if (l == -1) {
                if (v[j].first < v[i].first && v[i].first < v[j].second) l = j;
            }
            if (r == -1) {
                if (v[j].first < v[i].second && v[i].second < v[j].second) r = j;
            }

            if (r != -1 && r != -1) break;
        }

        for (auto &x : st[i]) {
            if (l != -1) st[l].insert(x);
            if (r != -1) st[r].insert(x);
        }
        if (l != -1) st[l].insert(i);
        if (r != -1) st[r].insert(i);
    }
    for (int i = 1; i <= n; i++) ile[i] = st[i].size();

    mint licznik = 0;
    for (int i = 1; i <= n; i++) {
        int s = ile[i] + 1;

        mint xd = 0;
        for (int j = 1, sgn = 1; j < s; j++) {
            xd += newtwon(s - 1, j) * newtwon(n, j + 1) * factorial[j] * factorial[n - j - 1] * sgn;
            sgn *= -1;
        }

        licznik += factorial[n] - xd;
    }
    
    cout << licznik / factorial[n] << '\n';
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    
    factorial[0] = 1;
    for (int i = 1; i <= MAXN; i++) {
        factorial[i] = factorial[i - 1] * i;
    }

    int t = 1;
    // cin >> t;
    while (t--) solve();
}