arcoeflecha.cpp

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<ll> vll;

const ll inf = 0x3fffffffffffffff;

ll merge(vll & v)
{
	if (v.size() == 1) return 0;

	int sz = (int)v.size();

	vll a;
	vll b;

	for (int i = 0; i < sz/2; i++) a.push_back(v[i]);
	for (int i = sz/2 ; i < sz; i++) b.push_back(v[i]);

	ll an = merge(a);
	an += merge(b);

	a.push_back(-inf);
	b.push_back(-inf);

	int i = 0, j = 0;

	for (int ind = 0; ind < sz; ind++) {

		if (a[i] <= b[j]) {

			v[ind] = b[j];
			j++;
			an += (ll)a.size() - (ll)i - 1;
		
		} else if (a[i] > b[j]) {

			v[ind] = a[i];
			i++;
		}
	}

	return an;
}

int main()
{
	int n;
	cin >> n;

	vll v;

	ll a, b;
	for (int i = 0; i < n; i++) {

		cin >> a >> b;

		v.push_back(a*a + b*b);
	}

	ll resp = merge(v);

	cout << resp << "\n";

	return 0;
}