#include<bits/stdc++.h>
using namespace std ;
typedef long long ll ;
const int MAXN = 503 ;
const int MOD = 1e9 + 7 ;
// mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
int n ;
pair < int , int > a[ MAXN ] ;
int v[ 2 * MAXN ] ;
ll dp[ MAXN ][ 2 * MAXN ] ;
ll en[ MAXN ] , nw[ MAXN ] ;
ll inv[ MAXN ] ;
ll fastpow ( ll x , ll pw ) {
ll ret = 1 ;
while ( pw > 0 ) {
if ( ( pw % 2 ) == 0 ) {
x = ( x * x ) % MOD ;
pw /= 2 ;
}
else {
ret = ( ret * x ) % MOD ;
-- pw ;
}
}
return ret ;
}
set < int > s ;
void solve ( ) {
cin >> n ;
for ( int i = 1 ; i <= n ; ++ i ) {
cin >> a[ i ].first >> a[ i ].second ;
s.insert ( a[ i ].first ) ;
s.insert ( a[ i ].second + 1 ) ;
}
int k = 0 ;
for ( auto x : s ) {
v[ ++ k ] = x ;
}
for ( int i = 1 ; i < MAXN ; ++ i ) {
inv[ i ] = fastpow ( i , MOD - 2 ) ;
}
dp[ 0 ][ 0 ] = 1 ;
for ( int i = 0 ; i <= n ; ++ i ) {
en[ i ] = nw[ i ] = 1 ;
}
for ( int j = 1 ; j <= k ; ++ j ) {
for ( int i = 1 ; i <= n ; ++ i ) {
for ( int t = i ; t >= 1 ; -- t ) {
dp[ i ][ t ] = dp[ i - 1 ][ t ] ;
if ( a[ i ].first <= v[ j ] && v[ j + 1 ] <= a[ i ].second + 1 ) {
if ( v[ j + 1 ] - v[ j ] - t + 1 > 0 ) {
ll coef = 1 ;
coef = ( coef * ( v[ j + 1 ] - v[ j ] - t + 1 ) ) % MOD ;
coef = ( coef * inv[ t ] ) % MOD ;
if ( t > 1 ) {
dp[ i ][ t ] = ( dp[ i ][ t ] + dp[ i - 1 ][ t - 1 ] * coef ) % MOD ;
}
else {
dp[ i ][ t ] = ( dp[ i ][ t ] + en[ i - 1 ] * coef ) % MOD ;
}
}
}
nw[ i ] = ( nw[ i ] + dp[ i ][ t ] ) % MOD ;
}
}
for ( int i = 1 ; i <= n ; ++ i ) {
en[ i ] = nw[ i ] ;
}
}
cout << ( en[ n ] - 1 + MOD ) % MOD << "\n" ;
}
int main ( ) {
ios_base :: sync_with_stdio ( false ) ;
cin.tie ( NULL ) ;
int t = 1 ; // cin >> t ;
while ( t -- ) { solve ( ) ; }
return 0 ;
}
