#include<iostream>
#include<stdio.h>
#include<vector>
using namespace std;
typedef long long int lld;
#define MOD 1000000007
int main(){
int n;
cin>>n;
pair<lld,lld> arr[n];
for(int i=0;i<n;i++)cin>>arr[i].first>>arr[i].second;
vector<lld> DP[n];
lld responde=0;
for(int i=0;i<n;i++){
for(int j=arr[i].first;j<=arr[i].second;j++){
int ans=1;
if(j>arr[i].first){
ans+=DP[i][DP[i].size()-1];
}
for(int k=0;k<i;k++){
if(j>arr[k].second){
ans+=DP[k][DP[k].size()-1];
ans%=MOD;
}else if(j>arr[k].first){
ans+=DP[k][j-arr[k].first-1];
ans%=MOD;
}
}
ans%=MOD;
DP[i].push_back(ans);
//responde+=ans;
}
responde+=DP[i][DP[i].size()-1];
responde%=MOD;
}
/*for(int i=0;i<n;i++){
for(int j=arr[i].first;j<=arr[i].second;j++){
cout<<DP[i][j-arr[i].first]<<" ";
}cout<<endl;
}*/
cout<<responde<<endl;
return 0;
}
