1 #include<bits/stdc++.h>
 2 using namespace std;
 3 typedef pair<int,int> pr;
 4
 5 const int maxn = (1<<21)+5;
 6 const int mod = 1000000007;
 7 struct line{int l,r,num;}A[maxn];
 8 int cnt,n,im[maxn];
 9
10 void read(){
11     scanf("%d",&n);
12     for(int i=1;i<=n;i++)scanf("%d%d",&A[i].l,&A[i].r),A[i].num=i;
13     sort(A+1,A+n+1,[](line a,line b){return a.l < b.l;});
14 }
15
16 priority_queue<pr,vector<pr>,greater<pr> > pq;
17 priority_queue<int,vector<int>,greater<int> > s[maxn>>1],t[maxn>>1];
18 int um,rs[maxn],num;
19 void work(){
20     for(int i=1;i<=n;i++) s[i].push(A[i].r);
21     for(int i=1;i<=n;i++){
22         while(!pq.empty()){
23             pr k = pq.top(); if(k.first > A[i].l) break; pq.pop();
24             if(s[k.second].size() && s[k.second].top() == k.first) s[k.second].pop();
25             else t[k.second].pop();
26             if(!s[k.second].size() && !t[k.second].size()) cnt++;
27             else{
28                 if(!t[k.second].size()) {pq.push(make_pair(s[k.second].top(),k.second));continue;}
29                 if(!s[k.second].size()) {pq.push(make_pair(t[k.second].top(),k.second));continue;}
30                 if(s[k.second].size() && t[k.second].size())
31                     pq.push(make_pair(min(s[k.second].top(),t[k.second].top()),k.second));
32             }
33         }
34         if(pq.empty()){pq.push(make_pair(A[i].r,i));continue;}
35         um = i;int place = 0;num = 0;
36         while(!pq.empty()){pr k = pq.top();if(k.first < A[i].r) {rs[++num] = k.second;pq.pop();}else break;}
37         for(int j=1;j<=num;j++){
38             int zeta = rs[j];
39             if(s[zeta].size() && t[zeta].size() && s[zeta].top() < A[i].r && t[zeta].top() < A[i].r){
40                 puts("0");return;
41             }
42             int sum1 = s[um].size() + t[um].size(),sum2 = s[zeta].size()+t[zeta].size();
43             if(sum1 > sum2){
44                 if((s[zeta].size() && s[zeta].top() < A[i].r) ^ place){
45                     while(t[zeta].size()){s[um].push(t[zeta].top());t[zeta].pop();}
46                     while(s[zeta].size()){t[um].push(s[zeta].top());s[zeta].pop();}
47                 }
48                 else{
49                     while(s[zeta].size()){s[um].push(s[zeta].top());s[zeta].pop();}
50                     while(t[zeta].size()){t[um].push(t[zeta].top());t[zeta].pop();}
51                 }
52             }else{
53                 if((s[zeta].size() && s[zeta].top() < A[i].r) ^ place){
54                     while(t[um].size()){s[zeta].push(t[um].top());t[um].pop();}
55                     while(s[um].size()){t[zeta].push(s[um].top());s[um].pop();}
56                     place ^= 1;
57                 }else{
58                     while(s[um].size()){s[zeta].push(s[um].top());s[um].pop();}
59                     while(t[um].size()){t[zeta].push(t[um].top());t[um].pop();}
60                 }
61                 um = zeta;
62             }
63         }
64         if(!t[um].size())pq.push(make_pair(s[um].top(),um));
65         else if(!s[um].size()) pq.push(make_pair(t[um].top(),um));
66         else pq.push(make_pair(min(s[um].top(),t[um].top()),um));
67     }
68     while(!pq.empty()){cnt++;pq.pop();}
69     int ans = 1;while(cnt--){ans*=2;ans%=mod;}
70     printf("%d",ans);
71 }
72
73 int main(){
74     read();
75     work();
76     return 0;
77 }