复杂度为：缩点后点数的平方。可以通过此题。

提交记录: Link

gen :

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define xztx main
int n = 1e5;
int xztx(){
	freopen("dat.in","w",stdout);
	cout << n << " " << n / 2 << "\n";
	for(int i = 1;i <= n / 2;++ i) cout << i << " " << i + n / 2 << "\n";
	return 0;
}
/*
  ans:
  0.500000
 */