#include<bits/stdc++.h>
using namespace std;
const int MAX_ECOLE=501,INFINI=1000*1000*1000+7;
int nbEcole;
map<pair<int,int>,int> memo;
int mini[MAX_ECOLE],maxi[MAX_ECOLE];
int dyna(int idEcole,int maxMaint) {
if (idEcole==nbEcole+1) {
return 1;
}
int val=memo[make_pair(idEcole,maxMaint)];
if (val!=0) {
return val;
}
val=dyna(idEcole+1,maxMaint);
for (int i=max(maxMaint+1,mini[idEcole]);i<=maxi[idEcole];i++) {
val+=dyna(idEcole+1,i);
val%=INFINI;
}
memo[make_pair(idEcole,maxMaint)]=val;
return val;
}
int main() {
ios_base::sync_with_stdio(false);
cin>>nbEcole;
for (int i=1;i<=nbEcole;i++) {
cin>>mini[i]>>maxi[i];
}
cout<<(dyna(1,-1)+INFINI-1)%INFINI<<endl;
}
