#include <bits/stdc++.h>
using namespace std;
#define int long long int
#define double long double
#define print(a) for(auto x : a) cout << x << " "; cout << endl
const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;
inline int power(int a, int b, int mod=M) {
int x = 1;
a %= mod;
while (b) {
if (b & 1) x = (x * a) % mod;
a = (a * a) % mod;
b >>= 1;
}
return x;
}
//_ ***************************** START Below *******************************
vector<int> a;
vector<int> b;
int consistency(int n, int k){
vector<int> diff(n);
int sum = 0;
for(int i=0; i<n; i++){
diff[i] = b[i] - a[i];
sum += a[i];
}
sort(begin(diff), end(diff), greater<int>());
k = n-k;
int i = 0;
while(k>0){
sum += diff[i];
k--;
i++;
}
return sum;
}
int practice(int n, int k){
return 0;
}
void solve() {
int n, k;
cin>> n >> k;
a.resize(n);
for(int i=0; i<n; i++) cin >> a[i];
b.resize(n);
for(int i=0; i<n; i++) cin >> b[i];
cout << consistency(n, k) << endl;
}
int32_t main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
return 0;
}
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