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#include <bits/stdc++.h>
using namespace std;

#define mp make_pair
#define pb push_back
// #define st first
#define nd second
#define fi first
#define se second
#define vt vector
#define FOR(a, b, c)  for(int a=b; a<c; ++a)
#define all(a)     (a).begin(),(a).end()
#define sz(a)      (int)(a).size()

typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef vector<int> vi; 
typedef vector<ll> vll;
typedef pii PII;
typedef pll PLL;

constexpr ll nax = 5e5+6969, INF = 1e9+2137, mod = 1e9 + 7 ;
constexpr ld eps = 1e-9;

mt19937_64 rng(6969);
// mt19937_64 rng(chrono::system_clock::now().time_since_epoch().count());

inline ll rand(ll l, ll r) {
	return uniform_int_distribution<ll>(l, r)(rng);
}

int n, nr = 1, vis[nax], lef[nax], rig[nax];
ll ans; 
vector<pii> v;

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

void flood(int x) {
    vis[x] = nr; 
    // ans++; 
    if(lef[x] != -1 && vis[lef[x]] < nr) {
        flood(lef[x]); 
    }
    if(rig[x] != -1 && vis[rig[x]] < nr) {
        flood(rig[x]); 
    }
}

int32_t main() {
    // ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    scanf("%d", &n); 
    for(int i = 0; i <= n; i++)  {
        lef[i] = rig[i] = -1; 
    }
    v.resize(n); 
    for(auto &e: v) {
        scanf("%d%d", &e.fi, &e.se); 
    }

    for(int i = n - 1; i >= 0; i--) {
        for(int j = i - 1; j >= 0; j--) {
            if(v[j].fi <= v[i].fi && v[i].fi <= v[j].se) {
                lef[i] = j; 
                break;
            }
        }

        for(int j = i - 1; j >= 0; j--) {
            if(v[j].fi <= v[i].se && v[i].se <= v[j].se) {
                rig[i] = j; 
                break;
            }
        }
    }

    // for(int i = 0; i < n; i++) {
    //     printf("%d %d\n", lef[i], rig[i]); 
    // }

    vi perm; 
    for(int i = 0; i < n; i++) {
        perm.pb(i); 
    }

    ll fact = 0; 

    do{

        // cout << "\n"; 
        // for(auto e: perm) 
        //     cout << e+1 << " "; 
        //     cout << "\n"; 

        for(auto ord: perm) {
            if(vis[ord] < nr) {
                ans++; 
                flood(ord); 
            }
        }
        nr++; 
        fact++; 
        // cout << "ans = " << ans << "\n"; 
    }while(next_permutation(all(perm)));
    
    // cout << ans << " " << fact << "\n"; 
    ans = (ans * Pow(fact, mod - 2)) % mod; 
    printf("%lld\n", ans);  


    return 0;
}