#include <bits/stdc++.h>
using namespace std;
// macros
typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef pair<ll, ll> lll;
typedef tuple<int, int, int> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<iii> viii;
typedef vector<ll> vll;
typedef vector<lll> vlll;
#define REP(a,b,c) for(int a=int(b); a<int(c); a++)
#define RE(a,c) REP(a,0,c)
#define RE1(a,c) REP(a,1,c+1)
#define REI(a,b,c) REP(a,b,c+1)
#define REV(a,b,c) for(int a=int(c-1); a>=int(b); a--)
#define FOR(a,b) for(auto& a : b)
#define all(a) a.begin(), a.end()
#define INF 1e18
#define EPS 1e-9
#define pb push_back
#define popb pop_back
#define fi first
#define se second
#define sz size()
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
// input
template<class T> void IN(T& x) {cin >> x;}
template<class H, class... T> void IN(H& h, T&... t) {IN(h); IN(t...); }
// output
template<class T1, class T2> void OUT(const pair<T1,T2>& x);
template<class T> void OUT(const vector<T>& x);
template<class T> void OUT(const T& x) {cout << x;}
template<class H, class... T> void OUT(const H& h, const T&... t) {OUT(h); OUT(t...); }
template<class T1, class T2> void OUT(const pair<T1,T2>& x) {OUT(x.fi,' ',x.se);}
template<class T> void OUT(const vector<T>& x) {RE(i,x.size()) OUT(i==0?"":" ",x[i]);}
template<class... T> void OUTL(const T&... t) {OUT(t..., "\n"); }
template<class H> void OUTLS(const H& h) {OUTL(h); }
template<class H, class... T> void OUTLS(const H& h, const T&... t) {OUT(h,' '); OUTLS(t...); }
//===================//
// Added libraries //
//===================//
// mod library
ll MOD=1e9+7;
inline ll mod(ll x_) {
return (x_)%MOD;
}
ll modpow(ll x_, ll N_) {
if(N_ == 0) return 1;
ll a = modpow(x_,N_/2);
a = (a*a)%MOD;
if(N_%2) a = (a*x_)%MOD;
return a;
}
ll inv(ll x_) {
return modpow(x_, MOD-2);
}
class mi {
public:
mi(ll v=0) {value = v;}
mi operator+ (ll rs) {return value+rs;}
mi operator- (ll rs) {return mod(value-rs+MOD);}
mi operator* (ll rs) {return mod(value*rs);}
mi operator/ (ll rs) {return mod(value*inv(rs));}
mi& operator+=(ll rs) {*this = (*this)+rs; return *this;}
mi& operator-=(ll rs) {*this = (*this)-rs; return *this;}
mi& operator*=(ll rs) {*this = (*this)*rs; return *this;}
mi& operator/=(ll rs) {*this = (*this)/rs; return *this;}
operator ll&() {return value;}
ll value;
};
typedef vector<mi> vmi;
//===================//
//end added libraries//
//===================//
void program();
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
program();
}
//===================//
// begin program //
//===================//
const int MX = 1010;
int n, m;
int a[MX], b[MX];
mi dp[MX][MX];
mi DIV[MX];
vi cc;
ll len[MX];
mi get(int i, int j) {
if(i < 0) return 1;
if(j < 0) return 0;
return dp[i][j];
}
void program() {
IN(n);
RE(i,n) IN(a[i], b[i]);
RE(i,n) b[i]++;
// coördinate compression
RE(i,n) cc.pb(a[i]), cc.pb(b[i]);
sort(all(cc));
cc.erase(unique(all(cc)),cc.end());
RE(i,n) a[i] = lower_bound(all(cc),a[i])-cc.begin();
RE(i,n) b[i] = lower_bound(all(cc),b[i])-cc.begin();
m = cc.size();
RE(i,m-1) len[i] = cc[i+1]-cc[i];
RE(i,MX) DIV[i] = mi(1)/mi(i);
RE(i,n) RE(j,m) {
dp[i][j] = get(i,j-1);
if(a[i] <= j && j < b[i]) {
ll inRange = 1;
mi mult = len[j];
REV(k,-1,i) {
dp[i][j] += get(k,j-1)*mult;
if(k == -1) continue;
if(a[k] <= j && j < b[k]) {
mult *= mi(inRange+len[j])*DIV[inRange+1];
inRange++;
}
}
dp[i][j] %= MOD;
}
}
mi ans = 0;
RE(i,n) ans += dp[i][m-1];
ans %= MOD;
OUTL((ll)ans);
}
