#include <bits/stdc++.h>
#define mp make_pair
#define pb push_back
#define pii pair<int,int>
#define LL long long
#define st first
#define nd second
#define endl '\n'
using namespace std;
const int MAXN=1000005;
int n,ans=1,mod=1e9+7,col[2][MAXN*8],t1,t2,beg[MAXN*2];
void upd(int x,int l,int r,int ll,int v,int c) {
if(l==ll&&r==ll) {
col[c][x]+=v;
return;
}
int md=(l+r)/2;
if(ll<=md)
upd(x*2,l,md,ll,v,c);
else upd(x*2+1,md+1,r,ll,v,c);
col[c][x]=col[c][x*2]+col[c][x*2+1];
}
int que(int x,int l,int r,int ll,int rr,int c) {
if(l>rr||r<ll)
return 0;
if(l>=ll&&r<=rr)
return col[c][x];
int md=(l+r)/2;
return que(x*2,l,md,ll,rr,c)+que(x*2+1,md+1,r,ll,rr,c);
}
void add(int x,int c) {
upd(1,1,n+n,beg[x],-1,c);
upd(1,1,n+n,x,1,c);
}
int main() {
scanf("%d",&n);
for(int i=1;i<=n;++i) {
scanf("%d %d",&t1,&t2);
beg[t2]=t1;
}
for(int i=1;i<=n+n;++i) {
if(beg[i]==0)
continue;
t1=que(1,1,2*n,beg[i],i,0);
t2=que(1,1,2*n,beg[i],i,1);
//cout<<i<<" "<<beg[i]<<" "<<t1<<" "<<t2<<endl;
if(t1&&t2) {
cout<<0<<endl;
return 0;
}
else if(t1==0&&t2==0) {
ans=(ans*2)%mod;
add(i,0);
}
else if(t1) {
add(i,1);
}
else {
add(i,0);
}
}
printf("%d\n",ans);
}
