#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 * 4;
inline int get() {
  int x;
  cin >> x;
  return x;
}
inline long long getlong() {
  long long x;
  cin >> x;
  return x;
}
inline string getString() {
  string s;
  cin >> s;
  return s;
}
template <typename T>
inline vector<T> getvector(int len) {
  vector<T> a(len);
  for (auto &it : a) cin >> it;
  return a;
}
inline vector<int> getvector(int len) {
  vector<int> a(len);
  for (auto &it : a) cin >> it;
  return a;
}
inline vector<pair<int, int>> getvector_andPairCnt(int len) {
  vector<pair<int, int>> a(len);
  int i = 1;
  for (auto &it : a) {
    it.second = i;
    i++;
    cin >> it.first;
  }
  return a;
}
double power_log(double power, double val) { return log(val) / log(power); }
template <typename T>
int sqr(T x) {
  return x * x;
}
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
  for (auto it : v) os << it << " ";
  os << "\n";
  return os;
}
template <typename T, typename H>
inline vector<pair<T, H>> getvector_andBiPair(int len) {
  vector<pair<T, H>> a(len);
  int i = 1;
  for (auto &it : a) {
    cin >> it.first >> it.second;
  }
  return a;
}
template <typename T>
inline set<T> vector_to_set(const vector<T> &vec) {
  set<T> s;
  for (auto &it : vec) s.insert(it);
  return s;
}
int main() {
  int n = get(), k = get();
  vector<pair<int, int>> arr(n);
  for (auto &it : arr) cin >> it.first;
  for (auto &it : arr) cin >> it.second;
  sort(arr.begin(), arr.end(), [](pair<int, int> l, pair<int, int> r) {
    return l.first - l.second < r.first - r.second;
  });
  int ans = 0;
  bool can = true;
  for (int i = 1; i <= n; i++) {
    if (i > k && arr[i - 1].first > arr[i - 1].second) {
      can = false;
    }
    if (can)
      ans += arr[i - 1].first;
    else
      ans += arr[i - 1].second;
  }
  cout << ans;
}
