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//2024-03-17
//author: Marcin Rolbiecki
#include <bits/stdc++.h>
using namespace std;

#define ll long long

const int maxN = 5e5 + 2;
const ll mod = 1e9 + 7;

int n;
int l[maxN], r[maxN], ile[maxN];
ll fac[maxN], invFac[maxN];
vector <int> G [maxN];

ll fastpow (ll a, ll b)
{
	ll res = 1;
	while (b)
	{
		if (b & 1)
		{
			res = (res * a) % mod;
		}
		a = (a * a) % mod;
		b >>= 1;
	}
	return res;
}

ll modInv (ll a)
{
	return fastpow(a, mod - 2);
}

ll choose (ll a, ll b)
{
	return fac[a] * invFac[b] % mod * invFac[a-b] % mod;
}

ll formula (ll i)
{
	return choose(n, ile[i]+1) * fac[ ile[i] ] % mod
			* fac[n - ile[i] - 1] % mod;
}

void prec ()
{
	fac[0] = 1;
	for (int i = 1; i < maxN; i++)
	{
		fac[i] = fac[i - 1] * i % mod;
	}
	
	invFac[maxN - 1] = modInv(fac[maxN-1]);
	
	for (int i = maxN-2; i >= 0; i--)
	{
		invFac[i] = invFac[i + 1] * (i + 1) % mod;
	}
}

int vis[maxN];

void dfs (int u, int root)
{
	vis[u] = root;
	
	for (int v : G[u]) 
	{
		if (vis[v] != root)
		{
			ile[v]++;
			dfs(v, root);
		}
	}
}

int main () {
		
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	
	prec();
	
	cin >> n;
	for (int i = 1; i <= n; i++)
	{
		cin >> l[i] >> r[i];
	}
		
	for (int i = n; i >= 1; i--)
	{
		for (int j = i-1; j >= 1; j--)
		{
			if (l[j] < l[i] && l[i] < r[j])
			{
				G[i].push_back(j);
				break;
			}
		}
		for (int j = i-1; j >= 1; j--)
		{
			if (l[j] < r[i] && r[i] < r[j])
			{
				G[i].push_back(j);
				break;
			}
		}
		if (G[i].size() == 2 && G[i][0] == G[i][1])
		{
			G[i].pop_back();
		}
	}
	
	for (int i = 1; i <= n; i++)
	{
		dfs(i, i);
	}
	
	ll ans = 0;
	for (int i = 1; i <= n; i++)
	{
		ans = (ans + formula(i)) % mod;
	}
	ans = ans * invFac[n] % mod;
	
	cout << ans;
	
	return 0;
}