// only miss the sun when it starts to snow
#include<bits/stdc++.h>
#define F first
#define S second
#define PB push_back
#define sz(s) int((s).size())
#define bit(n,k) (((n)>>(k))&1)
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
const int maxn=2e6+10,mod=1e9+7;
const ll inf=1e18;
int par[maxn], who[maxn], n;
bool st[maxn], bad=0;
vector<int> v[4*maxn];
pair<int,bool> Find(int u){
if(par[u]<0) return {u,0};
pair<int,bool> a= Find(par[u]);
a.S^= st[u];
par[u]= a.F, st[u]= a.S;
return {par[u],st[u]};
}
void Merge(int a,int b){
if(a==b) return;
pair<int,bool> A=Find(a), B=Find(b);
if(A.F == B.F){
bad|= A.S==B.S;
return;
}
if( par[A.F] > par[B.F] ) swap(A,B);
par[A.F]+=par[B.F];
par[B.F]= A.F;
st[B.F]= A.S ^ B.S ^ 1;
}
void build(int l=0,int r=maxn, int id=1){
if(r-l==1){
if(who[l] != 0) v[id].PB( who[l] );
return;
}
int mid=(l+r)>>1;
build(l,mid,2*id);
build(mid,r,2*id+1);
v[id].resize( sz(v[2*id]) + sz(v[2*id+1]) );
merge( v[2*id].begin(), v[2*id].end(), v[2*id+1].begin(), v[2*id+1].end(), v[id].begin() );
}
void mrg(int f,int s,int l=0,int r=maxn,int id=1){
if(f>=s || l>=r|| s<=l || r<=f) return;
if(f<=l && r<=s){
int mx=-1;
while(sz(v[id]) && s<v[id].back() ) Merge(v[id].back(), s), mx=max(mx, v[id].back() ), v[id].pop_back();
if(mx!=-1) v[id].PB(mx);
return;
}
int mid=(l+r)>>1;
mrg(f,s,l,mid,2*id), mrg(f,s,mid,r,2*id+1);
}
int main(){
ios_base::sync_with_stdio(false);cin.tie(0);
memset(par,-1,sizeof par);
cin>>n;
for(int i=0;i<n;i++){
int a,b; cin>>a>>b;
who[a]= b;
}
build();
for(int i=1;i<=2*n;i++){
if(who[i]!=0){
mrg(i,who[i]);
}
}
if(bad) return cout<<0<<endl,0;
int ans=1;
for(int i=1;i<=2*n;i++){
if(who[i]!=0 && Find(who[i]).F == who[i] ){
ans= 2ll*ans %mod;
}
}
return cout<<ans<<endl,0;
}
// Deathly mistakes:
// * Read the problem curfully.
// * Check maxn.
// * Overflows.
// #pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
