#include <bits/stdc++.h>
using namespace std;

int main() {
	int n;
	cin>>n;
	vector<int> arr1;
	vector<int> arr2;
	int k;
	cin>>k;
	int result=0;
	for(int i=0;i<n;i++)
	{
		int element;
		cin>>element;
		arr1.push_back(element);
	}
	for(int i=0;i<n;i++)
	{
		int element;
		cin>>element;
		arr2.push_back(element);
	}
	sort(arr1.begin(), arr1.end());
	sort(arr2.begin(), arr2.end());
	for(int j=n-1;j>=k-1;j--){
		result = result + arr1[j]*arr2[j];
	}
	cout<<result;
	return 0;
}