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#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair <int, int>;
using pll = pair <ll, ll>;
using pil = pair <int, ll>;
const int inf = 1e9+7;
const ll inf_ll = 1e18+7;

void boost() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
}

int n, l[500007], r[5000007], polka[500007];
bool odw[500007];
ll suma, liczba_permutacji, mod = 1e9+7;
vector<int> g[500007], permutacja;

ll potega(ll base, ll pot) {
    if (pot == 0)
        return 1;
    ll pom = potega(base, pot / 2);
    pom = (pom * pom) % mod;
    if (pot % 2 == 0)
        return pom;
    return (pom * base) % mod;
}

void dfs(int v) {
    odw[v] = true;
    for (int u: g[v]) {
        if (!odw[u])
            dfs(u);
    }
}

int main() {
    boost();

    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> l[i] >> r[i];
        if (polka[l[i]] != 0)
            g[i].push_back(polka[l[i]]);
        if (polka[r[i]] != 0)
            g[i].push_back(polka[r[i]]);
        for (int j = l[i]; j <= r[i]; j++)
            polka[j] = i;

        permutacja.push_back(i);
    }

    do {
        for (int i = 1; i <= n; i++)
            odw[i] = false;

        ll ile = 0;
        for (int x: permutacja) {
            if (!odw[x]) {
                dfs(x);
                ile++;
            }
        }

        suma += ile;
        suma %= mod;

        liczba_permutacji++;
        liczba_permutacji %= mod;
    } while (next_permutation(permutacja.begin(), permutacja.end()));

    cout << (suma * potega(liczba_permutacji, mod - 2)) % mod << "\n";

    return 0;
}