#include <bits/stdc++.h>
using namespace std;
struct PR {
  int to;
  int ne;
} Prise[200010];
bool compare(PR a, PR b) { return (a.to - a.ne) < (b.to - b.ne); }
int main(int argc, char const *argv[]) {
  int n, k;
  cin >> n >> k;
  int i;
  for (i = 0; i < n; i++) {
    cin >> Prise[i].to;
  }
  for (i = 0; i < n; i++) {
    cin >> Prise[i].ne;
  }
  sort(Prise, Prise + n, compare);
  int count = 0;
  for (i = 0; i < k; i++) {
    count += Prise[i].to;
  }
  for (i = k; i < n; i++) {
    if (Prise[i].to < Prise[i].ne) {
      count += Prise[i].to;
    } else {
      count += Prise[i].ne;
    }
  }
  cout << count << endl;
  return 0;
}
