/*
Wei Wai Wei Wai
Zumigat nan damu dimi kwayt rayt
*/
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double ld;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef complex<ld> point;
/*typedef __uint128_t L;
struct FastMod {
ull b, m;
FastMod(ull b) : b(b), m(ull((L(1) << 64) / b)) {}
ull reduce(ull a) {
ull q = (ull)((L(m) * a) >> 64);
ull r = a - q * b; // can be proven that 0 <= r < 2*b
return r >= b ? r - b : r;
}
};
FastMod FM(2);
*/
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
cerr << " " << H;
debug_out(T...);
}
#define debug(...) cerr << "(" << #__VA_ARGS__ << "):", debug_out(__VA_ARGS__)
#define all(x) x.begin(), x.end()
#define MP(x, y) make_pair(x, y)
#define F first
#define S second
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int maxn = 2e6 + 10;
const int inf = 1e9;
const int mod = 1e9 + 7;
int n, a[maxn];
pair<pii,pii> seg[maxn << 2];
vector<pii> ver[maxn];
pair<pii,pii> operator +(pair<pii,pii> a, pair<pii,pii> b){
return MP(min(a.F, b.F), max(a.S, b.S));
}
void build(int v, int l, int r){
if (l + 1 == r){
seg[v] = {{a[l], l}, {a[l], l}};
return;
}
int mid = (l + r) >> 1;
build(v << 1, l, mid);
build(v << 1 |1, mid, r);
seg[v] = seg[v << 1] + seg[v << 1 | 1];
}
void change(int v, int l, int r, int idx){
if (idx < l || r <= idx) return;
if (l + 1 == r){
seg[v] = {{idx, idx}, {idx, idx}};
return;
}
int mid = (l + r) >> 1;
change(v << 1, l, mid, idx);
change(v << 1 | 1, mid, r, idx);
seg[v] = seg[v << 1] + seg[v << 1 | 1];
}
pair<pii,pii> get(int v, int l, int r, int ql, int qr){
if (qr <= l || r <= ql) return {{inf, inf}, {0, 0}};
if (ql <= l && r <= qr) return seg[v];
int mid = (l + r) >> 1;
return get(v << 1, l, mid, ql, qr)
+ get(v << 1 | 1, mid, r, ql, qr);
}
void bfs(pii st){
change(1, 1, 2*n+1, st.F);
change(1, 1, 2*n+1, st.S);
ver[0].push_back(st);
for (int i = 0; i < n; i++){
if (ver[i].empty()) break;
vector<int> tmp, val;
for (auto [x, y]: ver[i]){
tmp.push_back(x);
tmp.push_back(y);
}
sort(all(tmp));
for (auto x: tmp){
if (a[x] > x) val.push_back(x);
else if (val.empty() || val.back() != a[x]){
cout << "0\n";
exit(0);
}
else val.pop_back();
}
for (auto x: ver[i]){
pair<pii,pii> tmp = get(1, 1, 2*n+1, x.F, x.S + 1);
while(tmp.F.F < x.F || tmp.S.F > x.S){
if (tmp.F.F < x.F){
ver[i+1].push_back(tmp.F);
change(1, 1, 2*n+1, tmp.F.F);
change(1, 1, 2*n+1, tmp.F.S);
}
if (tmp.S.F > x.S){
ver[i+1].push_back({tmp.S.S, tmp.S.F});
change(1, 1, 2*n+1, tmp.S.F);
change(1, 1, 2*n+1, tmp.S.S);
}
tmp = get(1, 1, 2*n+1, x.F, x.S+1);
}
}
ver[i].clear();
}
}
int main(){
ios_base::sync_with_stdio(false); cin.tie(0);
cin >> n;
for (int i = 1; i <= n; i++){
int l, r; cin >> l >> r;
a[l] = r;
a[r] = l;
}
build(1, 1, 2*n+1);
int ans = 1;
for (int i = 1; i <= 2*n; i++){
pair<pii,pii> tmp = get(1, 1, 2*n+1, i, i+1);
if (tmp.F.F != i){
ans = 2 * ans % mod;
bfs({min(tmp.F.F, tmp.F.S), max(tmp.F.F, tmp.F.S)});
}
}
cout << ans << '\n';
return 0;
}
