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

template <unsigned M> struct modular {
  using m = modular;
  unsigned v;
  modular(long long x = 0) : v((x %= M) < 0 ? x + M : x) {}
  m operator-() const { return m() -= *this; }
  m& operator+=(m b) { if ((v += b.v) >= M) v -= M; return *this; }
  m& operator-=(m b) { if (v < b.v) v += M; v -= b.v; return *this; }
  m& operator*=(m b) { v = (uint64_t)v * b.v % M; return *this; }
  m& operator/=(m b) { return *this *= power(b, M - 2); }
  friend m operator+(m a, m b) { return a += b; }
  friend m operator-(m a, m b) { return a -= b; }
  friend m operator*(m a, m b) { return a *= b; }
  friend m operator/(m a, m b) { return a /= b; }
  friend bool operator==(m a, m b) { return a.v == b.v; }
  friend string to_string(m a) { return to_string(a.v); }
};

constexpr long long mod = 1e9 + 7;
using mint = modular<mod>;

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  vector<pair<int, int>> p(n);
  for (auto&& e : p) {
    cin >> e.first >> e.second;
    e.first ^= 1;
    e.second -= e.first == 0;
  }
  sort(begin(p), end(p));
  vector<int> a(n), b(n);
  for (int i = 0; i < n; ++i) {
    a[i] = upper_bound(begin(p), end(p), make_pair(0, i)) - begin(p);
    b[i] = upper_bound(begin(p), end(p), make_pair(1, i)) - begin(p);
  }
  int m = *max_element(begin(a), end(a));
  assert(*min_element(begin(b), end(b)) == m);
  vector<mint> dp(m + 1);
  dp[0] = 1;
  for (int i = 0; i < n; ++i) {
    vector<mint> ndp(m + 1);
    for (int x = 0; x <= m; ++x) {
      if (x < m) {
        ndp[x + 1] += dp[x] * (a[i] - x);
      }
      ndp[x] += dp[x] * (m + i - x - b[i] + 1);
    }
    swap(dp, ndp);
  }
  cout << dp[m].v << '\n';
}