#ifdef LOCKAL
#define _GLIBCXX_DEBUG
#endif
#ifndef LOCKAL
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("unroll-all-loops")
#endif
#include <bits/stdc++.h>
//#define TIMUS
//#define FILENAME "journey"
#ifndef TIMUS
#include <ext/rope>
#include <ext/pb_ds/assoc_container.hpp>
#endif // TIMUS
#define all(x) x.begin(), x.end()
#define F first
#define S second
#define pb push_back
#define pii pair<int, int>
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
const int INF = INT_MAX / 2;
const ll LINF = (ll)2e18 + 666, M = 1e9 + 7;
const ld EPS = 1e-7;
#ifndef M_PI
const ld M_PI = acos(-1);
#endif // M_PI
using namespace std;
#ifndef TIMUS
using namespace __gnu_cxx;
using namespace __gnu_pbds;
template<class K, class T>
using ordered_map = tree<K, T, less<K>, rb_tree_tag, tree_order_statistics_node_update>;
template<class T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#endif
void run();
template<class T1, class T2>
inline bool mini(T1 &a, T2 b)
{
if (a > b)
{
a = b;
return 1;
}
return 0;
}
template<class T1, class T2>
inline bool maxi(T1 &a, T2 b)
{
if (a < b)
{
a = b;
return 1;
}
return 0;
}
int main()
{
#ifndef LOCKAL
#ifdef FILENAME
freopen(FILENAME".in", "r", stdin);
freopen(FILENAME".out", "w", stdout);
#endif // FILENAME
#endif
#ifndef TIMUS
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
#endif // TIMUS
srand(time(0));
auto start = clock();
run();
#ifdef LOCKAL
//cout << endl;
cout << "\ntime = " << (ld)(clock() - start) / CLOCKS_PER_SEC << "\n";
#endif
return 0;
}
//#define DEBUG
#if defined DEBUG && defined LOCKAL
#define debugdo(x) x
#else
#define debugdo(x)
#endif
#define debug_for(x) debug(#x": "); debugdo(for (auto &_x: x)) debug2(_x); debug("")
#define debug(x) debugdo(cout << x << endl)
#define debug2(x) debugdo(cout << x << " ")
// ---SOLUTION--- //
#define FAST 1e9
#ifdef FAST
char buf[(int)FAST];
size_t p = 0;
inline void *operator new(size_t n)
{
p += n;
return buf + p - n;
}
inline void operator delete(void *){}
#endif
struct min_f
{
static int neutral;
int operator()(int a, int b)
{
return min(a, b);
}
};
struct max_f
{
static int neutral;
int operator()(int a, int b)
{
return max(a, b);
}
};
int max_f::neutral;
int min_f::neutral;
template<class T, class F>
struct segtree
{
F f;
int n;
vector<T> a;
segtree(int n = 0): n(n), a(n * 4, F::neutral){}
void set(int p, T x, int v = 0, int l = 0, int r = -1)
{
if (r == -1)
r = n;
if (p < l || p >= r)
return;
if (r - l == 1)
{
a[v] = x;
return;
}
int c = (r + l) / 2;
set(p, x, v * 2 + 1, l, c);
set(p, x, v * 2 + 2, c, r);
a[v] = f(a[v * 2 + 1], a[v * 2 + 2]);
}
T get(int ql, int qr, int v = 0, int l = 0, int r = -1)
{
if (r == -1)
r = n;
if (ql >= r || l >= qr)
return F::neutral;
if (ql <= l && r <= qr)
return a[v];
int c = (r + l) / 2;
return f(get(ql, qr, v * 2 + 1, l, c), get(ql, qr, v * 2 + 2, c, r));
}
};
void run()
{
max_f::neutral = -INF;
min_f::neutral = INF;
int n;
cin >> n;
vector<int> a(n), b(n);
segtree<int, max_f> e(n * 2);
segtree<int, min_f> s(n * 2);
for (int i = 0; i < n; i++)
{
cin >> a[i] >> b[i];
a[i]--;
b[i]--;
e.set(a[i], b[i]);
s.set(b[i], a[i]);
}
vector<int> ev(n * 2);
for (int i = 0; i < n; i++)
{
ev[a[i]] = i + 1;
ev[b[i]] = -i - 1;
}
vector<char> use(n);
ll ans = 1;
for (int i = 0; i < n; i++)
{
if (!use[i])
{
ans = ans * 2 % M;
queue<int> q;
q.push(i);
while (!q.empty())
{
int v = q.front();
q.pop();
if (!use[v])
use[v] = 1;
debug("v = " << v);
debug(s.get(6, 7).F);
e.set(a[v], max_f::neutral);
s.set(b[v], min_f::neutral);
while (1)
{
bool f = 0;
auto x = e.get(a[v] + 1, b[v]);
if (x > b[v])
{
q.push(-ev[x] - 1);
use[-ev[x] - 1] = use[v] ^ 3;
debug(v << " - " << x.S);
e.set(a[-ev[x] - 1], max_f::neutral);
s.set(b[-ev[x] - 1], min_f::neutral);
f = 1;
}
x = s.get(a[v] + 1, b[v]);
if (x < a[v])
{
q.push(ev[x] - 1);
use[ev[x] - 1] = use[v] ^ 3;
debug(v << " - " << x.S);
e.set(a[ev[x] - 1], max_f::neutral);
s.set(b[ev[x] - 1], min_f::neutral);
f = 1;
}
if (!f)
break;
}
}
}
}
#define c use
for (auto &x: use)
x--;
debug_for(use);
{
stack<int> a, b;
for (auto x: ev)
{
if (x > 0)
{
if (c[x - 1])
a.push(x);
else
b.push(x);
}
else
{
x = -x;
if (c[x - 1])
{
if (a.top() != x)
{
cout << 0;
return;
}
a.pop();
}
else
{
if (b.top() != x)
{
cout << 0;
return;
}
b.pop();
}
}
}
cout << ans;
}
}
/*
43132142
*/
