#include<bits/stdc++.h>
#define int long long
using namespace std;
int dp[505][1005];
int a[505],b[505];
int md=1e9+7;
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
int n;cin>>n;
vector<int>val;
for(int i=1;i<=n;i++){
cin>>a[i]>>b[i];
val.push_back(a[i]);
val.push_back(b[i]);
}
sort(val.begin(),val.end());
val.erase(unique(val.begin(),val.end()),val.end());
for(int i=1;i<=n;i++){
a[i]=lower_bound(val.begin(),val.end(),a[i])-val.begin()+1;
b[i]=lower_bound(val.begin(),val.end(),b[i])-val.begin()+1;
}
//cerr<<"work\n";
dp[0][0]=1;
for(int i=1;i<=n;i++){
for(int j=0;j<=val.size();j++)dp[i][j]=dp[i-1][j];
for(int j=a[i];j<=b[i];j++){
for(int k=0;k<j;k++){
int r=val[j-1];
int l=0;
if(j-2>=0)l=val[j-2]+1;
l=max(l,val[a[i]-1]);
dp[i][j]+=(dp[i-1][k]*max(0ll,r-l+1))%md;
dp[i][j]%=md;
}
}
}
/*for(int i=1;i<=n;i++){
for(int j=0;j<=val.size();j++)cerr<<dp[i][j]<<" ";
cerr<<"\n";
}
cerr<<"work\n";*/
int ans=0;
for(int i=0;i<=val.size();i++){
ans+=dp[n][i];
ans%=md;
}
cout<<(ans-1+md)%md;
}
