#include <bits/stdc++.h> using namespace std; const int maxn = 1e6 + 100, mod = 1e9 + 7; pair <int, int> a[maxn]; int u[maxn], x[2 * maxn]; struct Node { int L, R, mid; pair <int, int> v; Node *lc, *rc; Node (int l, int r) { L = l, R = r, mid = (L + R) / 2, v = {0, 0}, lc = rc = NULL; return ; } void init() { if (R - L == 1) { v = {a[L].second, L}; return ; } lc = new Node(L, mid); rc = new Node(mid, R); lc->init(); rc->init(); v = max(lc->v, rc->v); return ; } void init2() { if (R - L == 1) { v = {x[L], x[L]}; return ; } lc = new Node(L, mid); rc = new Node(mid, R); lc->init2(); rc->init2(); v = max(lc->v, rc->v); return ; } void update (int p, int val = 0) { if (R - L == 1) { v = {val, 0}; return ; } if (p < mid) { lc->update(p, val); } else { rc->update(p, val); } v = max(lc->v, rc->v); return ; } pair <int, int> get(int l, int r) { if (l >= r) { return {-mod, -mod}; } if (l == L and R == r) { return v; } pair <int, int> ret = {-mod, -mod}; if (l < mid) { ret = max(ret, lc->get(l, min(r, mid))); } if (r > mid) { ret = max(ret, rc->get(max(l, mid), r)); } return ret; } }; Node *root[4]; bool mark[maxn][2]; void dfs(int v, bool s) { if (mark[v][s]) { return ; } mark[v][s] = 1; if (mark[v][s] and mark[v][s ^ 1]) { cout << 0; exit(0); } //cout << v << ' ' << s << endl; while (true) { pair <int, int> tmp = root[s]->get(v + 1, u[v]); if (tmp.first < a[v].second) { break; } root[s]->update(tmp.second); //cout << v << "-->" << tmp.second << endl; dfs(tmp.second, s ^ 1); } while (true) { int tmp = -root[2 + s]->get(a[v].first, a[v].second).first; //cout << v << " founr " << tmp << endl; if (tmp == 0 or tmp > v) { break; } root[2 + s]->update(a[tmp].second, -mod); //cout << v << "-->" << tmp << endl; dfs(tmp, s ^ 1); } return ; } int main() { ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0); int n; cin >> n; for (int i = 1;i <= 2 * n;i++) { x[i] = -mod; } for (int i = 1;i <= n;i++) { cin >> a[i].first >> a[i].second; } sort(a + 1, a + 1 + n); for (int i = 1;i <= n;i++) { u[i] = lower_bound(a + 1, a + 1 + n, make_pair(a[i].second, 0)) - a; x[a[i].second] = -i; } root[0] = new Node(1, n + 1); root[1] = new Node(1, n + 1); root[0]->init(); root[1]->init(); root[2] = new Node(1, 2 * n + 1); root[3] = new Node(1, 2 * n + 1); root[2]->init2(); root[3]->init2(); int ans = 1; for (int i = 1;i <= n;i++) { if (mark[i][0] or mark[i][1]) { continue; } ans = ans * 2 % mod; dfs(i, 0); } cout << ans; return 0; }