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// Karol Kosinski 2024
#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a),_b=(b);i<_b;++i)
#define FR_(i,a,b) for(int i=(a),_b=(b);i<=_b;++i)
#define FD_(i,b,a) for(int i=(b),_a=(a);i>=_a;--i)
#define ALL(c) (c).begin(),(c).end()
#define SIZE(c) int((c).size())
#define X first
#define Y second
#define endl '\n'
#define NAM(x) #x,'=',x
using namespace std;
using LL = long long;
using ULL = unsigned long long;
using PII = pair<int, int>;
using TIII = tuple<int, int, int>;
template<class...T> void _cout(T...a){(cout<<...<<a);}

#ifndef ENABLE_DEBUG
#define DEB(k,p,f,x...)
#else
#define DEB(k,p,f,x...) {if(k)_cout("------",setw(4),__LINE__," : ",__FUNCTION__,endl);if(p)f(x);}
#endif
#define DEBF(f,x...)    DEB(1,1,f,x)
#define DEBL            DEBF(void,0)
#define DEBC(p,x...)    DEB(0,p,_cout,x)
#define DEBUG(x...)     DEBC(1,x)

constexpr int NX = 500'005;
constexpr LL MOD = LL(1e9) + 7;

vector<int> G[NX], G2[NX];
bool On[NX];
int n, L[NX], R[NX], P[NX];

using PLL = pair<LL, LL>;

PLL gcd_fun(LL a, LL b)
{
    if ( b == 0 ) return PLL(1, 0);
    PLL t = gcd_fun( b, a % b );
    return PLL( t.Y, t.X - ( a / b ) * t.Y );
}

LL newton(int N, int K)
{
    LL num = 1, denom = 1;
    FD_(i,N,N-K+1)
    {
        num *= i;
        num %= MOD;
    }
    FD_(i,K,1)
    {
        denom *= i;
        denom %= MOD;
    }
    LL inv = gcd_fun(MOD, denom).Y + MOD;
    inv %= MOD;
    return ( num * inv ) % MOD;
}

void print_graph()
{
    FOR(i,0,n)
    {
        DEBUG( i, " : " );
        for ( int v : G2[i] ) DEBUG( v, ' ' );
        DEBUG( endl );
    }
}

LL recrun(int ind)
{
    int res = 0;
    if ( ind < n )
    {
        FOR(i,ind,n)
        {
            swap( P[i], P[ind] );
            res += recrun( ind + 1 );
            res %= MOD;
            swap( P[i], P[ind] );
        }
    }
    else
    {
        FOR(i,0,n)
        {
            int k = P[i];
            DEBUG( k, ' ' );
            if ( not On[k] )
            {
                ++ res;
                On[k] = true;
                for ( int v : G2[k] ) if ( not On[v] )
                {
                    On[v] = true;
                }
            }
        }
        FOR(i,0,n) On[i] = false;
        DEBUG( endl );
        DEBUG( NAM(res), endl );
    }
    return res;
}

LL testcase()
{
    cin >> n;
    FOR(i,0,n) cin >> L[i] >> R[i];
    FOR(i,0,n)
    {
        FD_(j,i-1,0)
        {
            if ( L[j] < L[i] and L[i] < R[j] )
            {
                G[i].push_back(j);
                DEBUG( "Added: (", i, ", ", j, ")", endl );
                break;
            }
        }
        FD_(j,i-1,0)
        {
            if ( L[j] < R[i] and R[i] < R[j] )
            {
                if ( G[i].empty() or G[i].front() != j )
                {
                    G[i].push_back(j);
                    DEBUG( "Added: (", i, ", ", j, ")", endl );
                }
                break;
            }
        }
    }
    FOR(i,0,n)
    {
        for ( int v : G[i] )
        {
            G2[i].push_back(v);
            for ( int x : G2[v] )
            {
                G2[i].push_back(x);
            }
        }
        sort( ALL( G2[i] ) );
        G2[i].erase( unique( ALL( G2[i] ) ), G2[i].end() );
    }
    DEBF( print_graph );
    FOR(i,0,n) P[i] = i;
    LL res = recrun( 0 );
    res %= MOD;
    LL denom = 1;
    FR_(i,1,n)
    {
        denom *= i;
        denom %= MOD;
    }
    DEBUG( "Final: ", NAM(res), endl );
    LL inv = gcd_fun(MOD, denom).Y + MOD;
    return ( res * inv ) % MOD;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << testcase() << endl;
    return 0;
}