#include <iostream> #include <vector> #include <set> #include <algorithm> using namespace std; int Mx[1<<21]; int main(){ int n, Ans = 1, mod = 1e9 + 7; cin>>n; vector<pair<int, int>> vec; for (int i=1, a, b;i<=n;i++){ cin>>a>>b; vec.push_back({a, b}); } sort(begin(vec), end(vec)); set<int> R; for (auto [l, r] : vec){ auto u = R.upper_bound(r); if (u != begin(R)) Mx[r] = *prev(u); if (Mx[r] < l) Ans = Ans * 2 % mod; if (Mx[r] > l and Mx[Mx[r]] > l) Ans = 0; R.insert(r); } cout<<Ans<<'\n'; }