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// Author: Kajetan Ramsza
#include "bits/stdc++.h"
using namespace std;

#define rep(i, a, b) for(int i = (a); i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

template<typename F, typename S> ostream& operator<<(ostream& os, const pair<F, S> &p) { return os<<"("<<p.first<<", "<<p.second<<")"; }
template<typename T> ostream &operator<<(ostream & os, const vector<T> &v) { os << "{"; typename vector< T > :: const_iterator it;
    for( it = v.begin(); it != v.end(); it++ ) { if( it != v.begin() ) os << ", "; os << *it; } return os << "}"; }

void dbg_out() { cerr<<'\n'; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cerr<<' '<<H; dbg_out(T...); }

#ifdef DEBUG
#define dbg(...) cerr<<"(" << #__VA_ARGS__ <<"):", dbg_out(__VA_ARGS__)
#else
#define dbg(...) 
#endif


const ll mod = 1000000007;

ll modpow(ll b, ll e) {
	ll ans = 1;
	for (; e; b = b * b % mod, e /= 2)
		if (e & 1) ans = ans * b % mod;
	return ans;
}

const int limit = int(5e5) + 7;
ll fact[limit], inv_fact[limit];

void preprocess() { 
	fact[0] = 1;
	rep(i,1,limit) fact[i] = fact[i-1] * i % mod;
	inv_fact[limit-1] = modpow(fact[limit-1], mod-2);
	for(ll i=limit-2;i>=0;i--) inv_fact[i] = inv_fact[i+1] * (i+1) % mod;
}

ll choose(int n, int k) {
	return (fact[n] * inv_fact[k] % mod) * inv_fact[n-k] % mod;
}

int n;
vector<pii> vec;
vector<bool> vis;
vi siz;
vector<vi> g;


int dfs_siz(int v) {
	int res = 1;
	vis[v] = true;
	for(auto e : g[v])
		if(!vis[e]) res += dfs_siz(e);
	return res;
}

ll calc_res(ll k) {
	if(k == 0) return fact[n];
	ll res = 0;
	for(ll i=k;i<=n-1;i++)
		res = (res + fact[i-1] * inv_fact[i-k] % mod * (n-i)) % mod;
	res = (res * fact[n-1-k]) % mod;
	res = (res * k) % mod;
	return res;	
}
ll result = 0;

int main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	preprocess();

	cin>>n;
	vec.resize(n);
	rep(i,0,n) cin>>vec[i].first>>vec[i].second;
	g.resize(n);

	rep(i,0,n) {
		for(int j=i-1;j>=0;j--)
			if(vec[j].first < vec[i].first && vec[i].first < vec[j].second) {
				g[j].push_back(i); break;
			}

		for(int j=i-1;j>=0;j--)
			if(vec[j].first < vec[i].second && vec[i].second < vec[j].second) {
				g[j].push_back(i); break;
			}
	}
	dbg(g);

	vis.resize(n);
	siz.resize(n);
	rep(i,0,n) {
		fill(all(vis), 0);
		siz[i] = dfs_siz(i);
		result = (result + calc_res(siz[i] - 1)) % mod;
	}
	dbg(result);
	cout<<(result * inv_fact[n] % mod)<<'\n';
}