#include <bits/stdc++.h>
using namespace std;
int modulo = 1e9 + 7;
int inf = 1e9;
int n, a[1000005], b[1000005];
int v1[2000005];///r-ul lui l de aici
int v2[2000005];///l-ul lui r de aici
int dude[2000005];
bool ok(vector<int> inds)
{
vector<pair<int, int>> w;
for (auto it : inds)
w.push_back({a[it], b[it]});
sort(w.begin(), w.end());
stack<int> stk;
for (auto it : w)
{
while (!stk.empty() and stk.top() < it.first)
stk.pop();
if (!stk.empty() and stk.top() < it.second)
return false;
stk.push(it.second);
}
return true;
}
pair<int, int> aint1[8000005], aint2[8000005];
void update1(int nod, int l, int r, int pos, pair<int, int> val)
{
if (l == r)
{
aint1[nod] = val;
return;
}
else
{
int mij = (l + r) / 2;
if (pos <= mij)
update1(2 * nod, l, mij, pos, val);
else
update1(2 * nod + 1, mij + 1, r, pos, val);
aint1[nod] = max(aint1[2 * nod], aint1[2 * nod + 1]);
}
}
void update2(int nod, int l, int r, int pos, pair<int, int> val)
{
if (l == r)
{
aint2[nod] = val;
return;
}
else
{
int mij = (l + r) / 2;
if (pos <= mij)
update2(2 * nod, l, mij, pos, val);
else
update2(2 * nod + 1, mij + 1, r, pos, val);
aint2[nod] = min(aint2[2 * nod], aint2[2 * nod + 1]);
}
}
pair<int, int> query1(int nod, int l, int r, int st, int dr)
{
if (r < st or dr < l)
return {-inf, 0};
else if (st <= l and r <= dr)
return aint1[nod];
else
{
int mij = (l + r) / 2;
return max(query1(2 * nod, l, mij, st, dr), query1(2 * nod + 1, mij + 1, r, st, dr));
}
}
pair<int, int> query2(int nod, int l, int r, int st, int dr)
{
if (r < st or dr < l)
return {inf, 0};
else if (st <= l and r <= dr)
return aint2[nod];
else
{
int mij = (l + r) / 2;
return min(query2(2 * nod, l, mij, st, dr), query2(2 * nod + 1, mij + 1, r, st, dr));
}
}
int find_inters(int x)
{
if (a[x] + 1 == b[x])
return -1;
int l = a[x] + 1, r = b[x] - 1;
//cout << l << ' ' << r << ' ';
pair<int, int> p1 = query1(1, 1, 2 * n, l, r), p2 = query2(1, 1, 2 * n, l, r);
//cout << p1.first << ' ' << p2.first << endl;
if (p1.first > r)
return p1.second;
else if (p2.first < l)
return p2.second;
else
return -1;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
cin >> n;
for (int i = 1; i <= n; i++)
cin >> a[i] >> b[i];
for (int i = 1; i <= 2 * n; i++)
v1[i] = -inf, v2[i] = inf;
for (int i = 1; i <= n; i++)
v1[a[i]] = b[i], v2[b[i]] = a[i], dude[a[i]] = dude[b[i]] = i;
for (int i = 1; i <= 2 * n; i++)
update1(1, 1, 2 * n, i, {v1[i], dude[i]});
for (int i = 1; i <= 2 * n; i++)
update2(1, 1, 2 * n, i, {v2[i], dude[i]});
set<int> s;
int ans = 1;
for (int i = 1; i <= n; i++)
s.insert(i);
while (!s.empty())
{
int x = *s.begin();
ans = ans * 2 % modulo;
queue<int> q1, q2;
vector<int> v1, v2;
q1.push(x);
v1.push_back(x);
update1(1, 1, 2 * n, a[x], {-inf, x});
update2(1, 1, 2 * n, b[x], {inf, x});
while (!q1.empty() or !q2.empty())
{
if (!q1.empty())
{
x = q1.front();
s.erase(x);
q1.pop();
while (true)
{
int y = find_inters(x);
//cout << x << ' ' << y << endl;
if (y == -1)
break;
else
{
q2.push(y);
v2.push_back(y);
update1(1, 1, 2 * n, a[y], {-inf, y});
update2(1, 1, 2 * n, b[y], {inf, y});
}
}
}
else
{
x = q2.front();
s.erase(x);
q2.pop();
while (true)
{
int y = find_inters(x);
//cout << x << ' ' << y << endl;
if (y == -1)
break;
else
{
//cout << x << ' ' << y << endl;
q1.push(y);
v1.push_back(y);
update1(1, 1, 2 * n, a[y], {-inf, y});
update2(1, 1, 2 * n, b[y], {inf, y});
}
}
}
}
if (!ok(v1) or !ok(v2))
{
ans = 0;
break;
}
}
cout << ans;
return 0;
}
