#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vii;
typedef pair<int,int> pi;
typedef vector<pi> pii;
typedef tuple<ll,ll,ll> ti;
typedef vector<ll> li;
typedef vector<li> lii;
#define REP(i,a,b) for(int i=a;i<b;i++)
#define F first
#define S second
#define PB push_back
#define LSOne(s) ((s)&(-s))
ll INF=1000000000000000010;
int inf=1e9+10;
ll M=1e9+7;
int main() {
// ios::sync_with_stdio(0);
// cin.tie(0);
int n;cin>>n;
vector<pair<ll,ll>> a(n);
vector<ll> md(n);
md[1]=1;
REP(i,2,n)md[i]=M-(M/i)*md[M%i]%M;
vector<ll> arr;
REP(i,0,n){
cin>>a[i].F>>a[i].S;
a[i].S++;
arr.PB(a[i].F);
arr.PB(a[i].S);
}
sort(arr.begin(),arr.end());
arr.erase(unique(arr.begin(),arr.end()),arr.end());
int m=arr.size();
vector<vector<ll>> dp(n,vector<ll>(m,0)),sm(n,vector<ll>(m,0));
vector<pair<int,int>> b(n);
REP(i,0,n){
b[i].F=lower_bound(arr.begin(),arr.end(),a[i].F)-arr.begin();
b[i].S=lower_bound(arr.begin(),arr.end(),a[i].S)-arr.begin();
}
REP(i,0,n){
REP(j,b[i].F,b[i].S){
dp[i][j]=arr[j+1]-arr[j];
sm[i][j]=1;
if(j!=0)REP(k,0,i){
sm[i][j]+=dp[k][j-1];
sm[i][j]%=M;
dp[i][j]+=dp[k][j-1]*(arr[j+1]-arr[j]);
dp[i][j]%=M;
}
ll N=arr[j+1]-arr[j]-1;
ll K=1;
ll tot=N;
for(int k=i-1;k>=0;k--){
if(sm[k][j]==0)continue;
N++;K++;
tot*=N;
tot%=M;
tot*=md[K];
tot%=M;
dp[i][j]+=tot*sm[k][j];
dp[i][j]%=M;
}
}
REP(j,1,m)dp[i][j]+=dp[i][j-1];
}
ll ans=0;
REP(i,0,n){
ans+=dp[i][m-1];
ans%=M;
}
cout<<ans;
}
