#include<bits/stdc++.h>
#define sqr(x) ((x)*(x))
#define ll long long
#define ull unsigned long long
#define ui unsigned int
#define ld long double
#define vi vector<int>
#define HEAP(...) priority_queue<__VA_ARGS__ >
#define heap(...) priority_queue<__VA_ARGS__,vector<__VA_ARGS__ >,greater<__VA_ARGS__ > > 
#define pii pair<int,int> 
#define pb push_back
#define mp make_pair
#define debuge cerr<<"isok"<<endl
#define debug(x) cerr<<#x<<"="<<x<<endl
#define dprintf(...) fprintf(stderr,__VA_ARGS__)
#define SS second
#define FF first
#define ls (k<<1)
#define rs (k<<1|1)
#define clr(a,x) memset(a,x,sizeof(a))
#define cpy(a,x) memcpy(a,x,sizeof(a))
#define file(x) freopen(x".in","r",stdin),freopen(x".out","w",stdout)
#define SZ(x) ((int)x.size())
#define dputs(...) fputs(__VA_ARGS__,stderr)
using namespace std;
template<class T> inline void gmin(T &x,const T &y){if(x>y) x=y;}
template<class T> inline void gmax(T &x,const T &y){if(x<y) x=y;}
const int BufferSize=1<<16;
char buffer[BufferSize],*Bufferhead,*Buffertail;
bool Terminal;
inline char Getchar(){
	if(Bufferhead==Buffertail){
		int l=fread(buffer,1,BufferSize,stdin);
		if(!l){Terminal=1;return 0;}
		Buffertail=(Bufferhead=buffer)+l;
	}
	return *Bufferhead++;
}
template<class T>inline bool read(T &x){
	x=0;char c=Getchar(),rev=0;
	while(c<'0'||c>'9'){c=Getchar();rev|=c=='-';if(Terminal)return 0;}
	while(c>='0'&&c<='9') x=x*10+c-'0',c=Getchar();
	if(c=='.'){
		c=Getchar();double t=0.1;
		while(c>='0'&&c<='9') x=x+(c-'0')*t,c=Getchar(),t=t/10;
	}
	x=rev?-x:x;
	return 1;
}
template<class T1,class T2> inline bool read(T1 &x,T2 &y){return read(x)&read(y);}
template<class T1,class T2,class T3> inline bool read(T1 &x,T2 &y,T3 &z){return read(x)&read(y)&read(z);}
template<class T1,class T2,class T3,class T4> inline bool read(T1 &x,T2 &y,T3 &z,T4 &w){return read(x)&read(y)&read(z)&read(w);}
inline bool reads(char *x){
	char c=Getchar();
	while(c<33||c>126){c=Getchar();if(Terminal)return 0;}
	while(c>=33&&c<=126) (*x++)=c,c=Getchar();
	*x=0;return 1;
}
template<class T>inline void print(T x,const char c='\n'){
	if(!x){putchar('0');putchar(c);return;}
	if(x<0) putchar('-'),x=-x;
	int m=0,a[20];
	while(x) a[m++]=x%10,x/=10;
	while(m--) putchar(a[m]+'0');
	putchar(c);
}
//--------------------------------head---------------------------------------------

const int inf=0x3f3f3f3f;
const int N=200005,M=100005,mod=1e9+7;
template<class T,class S> inline void ch(T &x,const S y){x=(x+y)%mod;}
inline int exp(int x,int y,const int mod=::mod){
	int ans=1;
	while(y){
		if(y&1) ans=(ll)ans*x%mod;
		x=(ll)x*x%mod;y>>=1;
	}return ans;
}

int n,fac[N],ifac[N];
struct node{int x,y;}ori[N<<1];
inline int C(int x,int y){
	if(x<y) return 0;
	return (ll)fac[x]*ifac[y]%mod*ifac[x-y]%mod;
}
inline bool cmp(node a,node b){return mp(a.x,a.y)<mp(b.x,b.y);}

int tcnt,cnt,root,w,dep[N],fa[N],val[N];
bool vis[N];
vector<pii> g[N],seq;
void add(int x,int y,int z){
//	dprintf("%d %d %d\n",x,y,z);
	g[x].pb(mp(y,z));g[y].pb(mp(x,z));
}
void dfs(int x){
	vis[x]=1;
	cnt++;tcnt-=2;
	for(auto i:g[x]){
		tcnt++;
		int y=i.FF;
		if(vis[y]){
			if(dep[y]>dep[x]){
				if(~w) continue;
				w=i.SS;
				while(y!=x)
					gmax(w,val[y]),y=fa[y];
			}
			continue;
		}
		dep[y]=dep[x]+1;fa[y]=x;val[y]=i.SS;
		dfs(y);
	}
}
inline pii dfs(int x,int f,int w){
//	dprintf("%d %d %d\n",x,f,w);
	int res=1,now=0;
	for(auto i:g[x]){
		int y=i.FF;
		if(y==root||y==f) continue;
		pii t=dfs(y,x,i.SS);
		if(i.SS>w) seq.pb(t);
		else{
			now+=t.SS;
			res=(ll)res*t.FF%mod*C(now,t.SS)%mod;
		}
	}
	return mp(res,now+1);
}
int solve(int w,int flag){
	int u=ori[w].x,v=ori[w].y+n;
	if(flag) swap(u,v);
	seq.clear();root=u;
	seq.pb(dfs(u,v,w));
	int now=0,res=1;
	for(auto i:seq) res=(ll)res*i.FF%mod*C(now+i.SS,i.SS)%mod,now+=i.SS;
//	for(auto i:seq) dprintf("%d %d\n",i.FF,i.SS);
//	dputs("\n");
	return res;
}

int main(){
#ifdef rqgao2014
	freopen("input.txt","r",stdin);
#endif
	n=200000;fac[0]=ifac[0]=1;
	for(int i=1;i<=n;i++) fac[i]=(ll)fac[i-1]*i%mod;
	ifac[n]=exp(fac[n],mod-2);
	for(int i=n-1;i;i--) ifac[i]=(ll)ifac[i+1]*(i+1)%mod;
	
	scanf("%d",&n);
	for(int i=1;i<=n*2;i++)
		scanf("%d%d",&ori[i].x,&ori[i].y);
	sort(ori+1,ori+n*2+1,cmp);
	for(int i=1;i<=n*2;i++)
		add(ori[i].x,ori[i].y+n,i);
	int ans=1,now=0;
	for(int i=1;i<=n*2;i++)
		if(!vis[i]){
			w=-1;tcnt=cnt=0;dfs(i);
			if(tcnt){puts("0");return 0;}
			now+=cnt;
//			debug(w);
			ans=(ll)ans*(solve(w,0)+solve(w,1))%mod*C(now,cnt)%mod;
		}
	printf("%d\n",ans);
	return 0;
}

Measured memory_bytes: 22776