#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
const int mxN = 500, M = 1e9+7;
int n, a[mxN], b[mxN];
ll dp[mxN+1][2*mxN], c[2*mxN][mxN+1];
vector<int>pts;
inline ll modI(ll a, ll m){ return a<=1?a:(1-modI(m%a,a)*m)/a+m; }
int main(){
ios::sync_with_stdio(0);
cin.tie(0); cin >> n;
for(int i=0;i<n;i++){
cin >> a[i] >> b[i], --a[i];
pts.pb(a[i]); pts.pb(b[i]);
}
sort(pts.begin(), pts.end());
pts.resize(unique(pts.begin(), pts.end())-pts.begin());
for(int i=1;i<pts.size();i++){
c[i][1] = pts[i]-pts[i-1];
for(int j=2;j<=n;j++) c[i][j]=c[i][j-1]*(pts[i]-pts[i-1]+j-1)%M*modI(j,M)%M;
}
for(int i=0;i<pts.size();i++) dp[0][i]=1;
for(int i=1;i<=n;i++){
dp[i][0] = 1;
for(int j=1;j<pts.size();j++){
dp[i][j] = dp[i][j-1];
for(int k=i,n2=0;k;k--){
if(pts[j]>a[k-1]and pts[j]<=b[k-1]){
++n2;
dp[i][j]+=dp[k-1][j-1]*c[j][n2]%M;
}
}
dp[i][j]%=M;
}
}
cout<<dp[n][pts.size()-1]-1<<endl;
}
