#include "cross.h"
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
long long SelectCross(int k, std::vector<int> a, std::vector<int> b) {
vector<pair<int,int> > x;
multiset<int> r;
for(int i = 0; i < (int)a.size(); i++){
x.push_back({a[i], b[i]});
}
sort(x.begin(), x.end());
reverse(x.begin(), x.end());
ll ans = 0;
multiset<int> bb;
for(pair<int,int> p : x){
bb.insert(p.second);
while((int)bb.size() > k) bb.erase(bb.begin());
if((int)bb.size() == k){
ll A = p.first;
ll B = *bb.begin();
ans = max(ans, 2 * A * B - A * A);
}
}
return ans;
}
