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

typedef long long int i64;

const i64 MOD = 1000000007;

struct Shelf {
  int left, right;
  std::set<int> connections;
} shelves[500500];

inline bool between(int middle, Shelf &s) { return s.left < middle && middle < s.right; }

int sim(std::vector<int> &order) {
  auto N = order.size();
  int res = 0;
  std::set<int> sunken;
  for (int k : order) {
    if (sunken.insert(k).second) {
      ++res;
      for (int n : shelves[k].connections) {
        sunken.insert(n);
      }
      if (sunken.size() == N) {
        break;
      }
    }
  }
  return res;
}

i64 nwd(i64 a, i64 b) {
  if (a % b == 0) {
    return b;
  }
  return nwd(b, a % b);
}

inline void swap(i64 &a, i64 &b) {
  i64 t = a;
  a = b;
  b = t;
}

i64 inv(i64 a, i64 mod) {
  i64 u = 1, w = a, x = 0, z = mod, q;
  while (w != 0) {
    if (w < z) {
      swap(u, x);
      swap(w, z);
    }
    q = w / z;
    u = u - q * x;
    w = w - q * z;
  }
  if (x < 0) {
    x = x + mod;
  }
  return x;
}

i64 frac(i64 sum, i64 opts) {
  i64 nn = nwd(sum, opts);
  sum /= nn;
  opts /= nn;
  if (opts == 1) {
    return sum;
  } else {
    i64 in = inv(opts, MOD);
    return (in * sum) % MOD;
  }
}

int main() {
  // printf("%lld\n", inv(30, MOD));
  // exit(0);

  int N;
  std::vector<int> order;
  scanf("%d", &N);
  for (int i = 0; i < N; ++i) {
    order.push_back(i);
    int cl, cr;
    scanf("%d%d", &cl, &cr);
    shelves[i].left = cl;
    shelves[i].right = cr;
    bool left_used = false, right_used = false;
    for (int j = i - 1; j >= 0; --j) {
      if (!left_used && between(cl, shelves[j])) {
        left_used = true;
        shelves[i].connections.insert(j);
        for (int next : shelves[j].connections) {
          shelves[i].connections.insert(next);
        }
      }
      if (!right_used && between(cr, shelves[j])) {
        right_used = true;
        shelves[i].connections.insert(j);
        for (int next : shelves[j].connections) {
          shelves[i].connections.insert(next);
        }
      }
    }
  }

  // for (int i = 0; i < N; ++i) {
  //   printf("%d: ", i + 1);
  //   for (int c : shelves[i].connections) {
  //     printf("%d ", c + 1);
  //   }
  //   puts("");
  // }
  i64 sum = 0;
  i64 opts = 0;

  do {
    ++opts;
    sum += sim(order);
    // for (int x : order) {
    //   printf("%d ", x + 1);
    // }
    // printf(" -> %d\n", sim(order));
  } while (std::next_permutation(order.begin(), order.end()));

  printf("%lld\n", frac(sum, opts));
  return 0;
}