#include using namespace std; using ll=long long; int main(){ int n; cin>>n; vector l(n),r(n); for(int i=0;i>l[i]>>r[i]; vector p(n); iota(p.begin(),p.end(),0); int ans=0; do{ int x=0; bool ok=true; for(int i=0;ir[p[i]])ok=false; else x=max(x,l[p[i]]); } if(ok)ans++; }while(next_permutation(p.begin(),p.end())); cout<