/*input
1 15
2 5
3 8
4 6
14 16
7 9
10 13
11 12
3
1 4
2 5
3 6
5
1 4
2 10
6 9
7 8
3 5
*/
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ld, ld> pd;
typedef vector<int> vi;
typedef vector<vi> vii;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<vl> vll;
typedef vector<pi> vpi;
typedef vector<vpi> vpii;
typedef vector<pl> vpl;
typedef vector<cd> vcd;
typedef vector<pd> vpd;
typedef vector<bool> vb;
typedef vector<vb> vbb;
typedef std::string str;
typedef std::vector<str> vs;
#define x first
#define y second
#define debug(...) cout<<"["<<#__VA_ARGS__<<": "<<__VA_ARGS__<<"]\n"
const int MOD = 1000000007;
const ll INF = std::numeric_limits<ll>::max();
const int MX = 100101;
const ld PI = 3.14159265358979323846264338327950288419716939937510582097494L;
template<typename T>
pair<T, T> operator+(const pair<T, T> &a, const pair<T, T> &b) { return pair<T, T>(a.x + b.x, a.y + b.y); }
template<typename T>
pair<T, T> operator-(const pair<T, T> &a, const pair<T, T> &b) { return pair<T, T>(a.x - b.x, a.y - b.y); }
template<typename T>
T operator*(const pair<T, T> &a, const pair<T, T> &b) { return (a.x * b.x + a.y * b.y); }
template<typename T>
T operator^(const pair<T, T> &a, const pair<T, T> &b) { return (a.x * b.y - a.y * b.x); }
template<typename T>
void print(vector<T> vec, string name = "") {
cout << name;
for (auto u : vec)
cout << u << ' ';
cout << '\n';
}
vi rankas;
vi p;
vi edges[(int)1e6];
vpi poros;
vi kas;
int N;
int findSet(int i) { return (p[i] == i) ? i : (p[i] = findSet(p[i])); }
bool isSameSet(int i, int j) { return findSet(i) == findSet(j); }
void unionSet(int i, int j) {
edges[kas[i]].emplace_back(kas[j]);
edges[kas[j]].emplace_back(kas[i]);
if (isSameSet(i, j)) {
printf("0\n");
exit(0);
}
int x = findSet(i), y = findSet(j);
if (rankas[x] > rankas[y]) p[y] = x;
else {
p[x] = y;
if (rankas[x] == rankas[y]) rankas[y]++;
}
}
vb been(1e6, false);
vi keliai[2];
vi kitas;
void dfs(int x, int h) {
been[x] = true;
keliai[h].emplace_back(poros[x].x);
keliai[h].emplace_back(poros[x].y);
h = 1 - h;
for (auto u : edges[x])
if (!been[u])
dfs(u, h);
}
bool blogas() {
for (int n = 0; n < N; ++n)
{
if (been[n]) continue;
keliai[0].clear();
keliai[1].clear();
dfs(n, 0);
sort(keliai[0].begin(), keliai[0].end());
sort(keliai[1].begin(), keliai[1].end());
// printf("n = %d\n", n);
// print(keliai[0], "keliai[0]: ");
// print(keliai[1], "keliai[1]: ");
stack<int> stak;
for (auto u : keliai[0]) {
if (u < kitas[u]) stak.push(kitas[u]);
else {
if (stak.top() != u) return true;
stak.pop();
}
}
for (auto u : keliai[1]) {
if (u < kitas[u]) stak.push(kitas[u]);
else {
if (stak.top() != u) return true;
stak.pop();
}
}
}
return false;
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> N;
p = vi(2 * N + 1); for (int i = 0; i <= 2 * N; i++) p[i] = i;
rankas = vi(2 * N + 1, 0);
kas = vi(2 * N + 1);
kitas = vi(2 * N + 1);
for (int i = 0; i < N; ++i)
{
int a, b;
cin >> a >> b;
kitas[a] = b;
kitas[b] = a;
unionSet(a, b);
kas[a] = kas[b] = i;
poros.emplace_back(a, b);
}
ll ats = 1;
// sort(poros.begin(), poros.end());
set<int> visos;
set<int> reikalingos;
for (int i = 1; i <= 2 * N; i++) {
if (i < kitas[i]) {
int a = i;
int b = kitas[i];
if (reikalingos.empty()) {
visos.insert(b);
reikalingos.insert(b);
continue;
}
auto it = reikalingos.begin();
int prad = *it;
if (b < prad) reikalingos.insert(b);
else {
while (it != reikalingos.end() and * it < b) {
// printf("jungiu i = %d, it = %d\n", i, *it);
unionSet(i, *it);
auto prev = it;
it = next(it);
reikalingos.erase(prev);
}
reikalingos.insert(prad);
}
visos.insert(b);
} else {
visos.erase(i);
reikalingos.erase(i);
if (visos.size())
reikalingos.insert(*visos.begin());
}
}
if (blogas()) {
printf("0\n");
return 0;
}
vb buvo(2 * N + 1, false);
for (int i = 1; i <= 2 * N; ++i)
{
if (!buvo[findSet(i)]) ats = (ats * 2) % MOD;
buvo[findSet(i)] = true;
}
printf("%lld\n", ats);
}
/* Look for:
* special cases (n=1?)
* overflow (ll vs int?)
* the exact constraints (multiple sets are too slow for n=10^6 :( )
* array bounds
*/
