#include <cstdio>
#include <cctype>
typedef long long ll;

template <typename _tp> inline void read(_tp&x){
	char ch=getchar(),ob=0;x=0;
	while(ch!='-'&&!isdigit(ch))ch=getchar();if(ch=='-')ob=1,ch=getchar();
	while(isdigit(ch))x=x*10+ch-'0',ch=getchar();if(ob)x=-x;
}

const int N = 201000;
struct Edge {int v, nxt;} a[N*4];
int head[N], Head[N], indeg[N];
int sz[N], pr[N];
bool vis[N];
int n, _;

inline void add(int x, int y, int*arr) {
	a[++_].v = y, a[_].nxt = arr[x], arr[x] = _;
}

const int p = 1e9+7;
int fac[N], ifac[N], inv[N];

int st[N], tp;
#define FID(i) for(int id=1,i;i=st[id],id<=tp;++id)

int X, Y;
int et, pt;

void bfs(int x, int las) {
	vis[st[++tp] = x] = true, ++pt;
	for(int i=head[x];i;++et,i=a[i].nxt)
		if(!vis[a[i].v]) bfs(a[i].v, x);
		else if(a[i].v != las) X = x, Y = a[i].v;
}

void tfs(int x, int las) {
	for(int i=head[x];i;i=a[i].nxt)
		if(a[i].v != las and a[i].v != X)
			pr[a[i].v] = x, tfs(a[i].v, x);
}

void dfs(int x, int las) {
	sz[x] = 1;
	for(int i=Head[x];i;i=a[i].nxt)
		if(a[i].v != las)
			dfs(a[i].v, x), sz[x] += sz[a[i].v];
}

int solve() {
	tfs(X, Y);
	pr[X] = Y;
	FID(i) Head[i] = indeg[i] = 0;
	FID(x) for(int i=head[x];i;i=a[i].nxt)
		if(a[i].v < pr[x]) add(x, a[i].v, Head), ++indeg[a[i].v];
	
	FID(i) if(!indeg[i]) dfs(i, i);
	int Ans = fac[pt];
	FID(i) Ans = (ll)Ans * inv[sz[i]]%p;
	return Ans;
}

int main() {
	read(n);
	for(int i=1,x,y;i<=(n<<1);++i) {
		read(x), read(y), y += n;
		add(x, y, head), add(y, x, head);
	}
	
	n <<= 1;
	fac[0] = fac[1] = inv[0] = inv[1] = ifac[0] = ifac[1] = 1;
	for(int i=2;i<=n;++i) {
		fac[i] = (ll)fac[i-1] * i%p;
		inv[i] = (ll)(p-p/i) * inv[p%i]%p;
		ifac[i] = (ll)ifac[i-1] * inv[i]%p;
	}
	
	int Ans = fac[n];
	for(int i=1;i<=n;++i)
		if(!vis[i]) {
			tp = pt = et = 0;
			bfs(i, i);
			Ans = (ll)Ans * ifac[pt]%p;
			if((pt << 1) != et) return puts("0"), 0;
			int res = solve();
			X ^= Y, Y ^= X, X ^= Y;
			res += solve();
			Ans = (ll)Ans * res%p;
		}
	printf("%d\n", Ans);
	return 0;
}