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#include <cstdio>
#include <algorithm>
#include <set>

using namespace std;

pair<int, int> tab[500001];

int p[500001];
int vis[500001];

set<int> z[500001];
int dodane[500001];

int MOD = 1000000007;

long long power(long long a, long long n)
{
  long long r = 1;
  while (n > 0)
  {
    if (n % 2 == 1)
      r *= a;
    r %= MOD;
    n /= 2;
    a = a * a % MOD;
  }
  return r;
}


int main()
{
  int n;
  scanf("%d", &n);
  
  for (int i = 0; i < n; i++)
  {
    scanf("%d %d", &tab[i].first, &tab[i].second);
    p[i] = i;
  }
  
  z[0].insert(0);
  
  for (int i = 1; i < n; i++)
  {
    z[i].insert(i);
    for (int j = i - 1; j >= 0; j--)
    {
      int l = tab[i].first;
      int r = tab[i].second;

      int l2 = tab[j].first;
      int r2 = tab[j].second;

      if (j == i - 1)
      {
        if (l < r2 && l > l2)
          z[i].insert(j);
        if (r > l2 && r < r2)
          z[i].insert(j);
        continue;
      }
      
      bool ok = true;
      for (int k = j + 1; k < i; k++)
        if (l < r2 && l > l2 && (l > tab[k].second || l < tab[k].first));
        else
        ok = false;
      if (ok)
       z[i].insert(j);

      ok = true;
      for (int k = j + 1; k < i; k++)
        if (r > l2 && r < r2 && (r > tab[k].second || r < tab[k].first));
        else
        ok = false;
      if (ok)
       z[i].insert(j);
    }
    int cnt = 0;
    for (auto it : z[i])
    {
      for (auto it2 : z[it])
      {
        dodane[cnt] = it2;
        cnt++;
      }
    }
    for (int j = 0; j < cnt; j++)
    {
      z[i].insert(dodane[j]);
    }
  }
 
  int a = 0;
  int b = 0;
  do {
    a++;
 
    for (int i = 0; i < n; i++)
    {
      vis[i] = 0;
    }
    int ret = 0;
    for (int i = 0; i < n; i++)
    {
      if (!vis[p[i]])
      {
        vis[p[i]] = 1;
        ret++;
        for (auto it : z[p[i]])
        {
          if (!vis[it])
          {
            vis[it] = 1;
          }
        }
      }
    }
    b += ret;
    
  } while (next_permutation(p, p + n));
  
  printf("%d\n", 1LL * power(a, MOD - 2) * b % MOD);
  
  return 0;
}