#include <iostream>
#include <algorithm>
using namespace std;
struct data{
int x, y, z;
};
int n, k, a[200005], b[200005];
data f[200005];
bool cmp(data d1, data d2){
return (d1.x < d2.x);
}
int main(){
cin >> n >> k;
for (int i = 1; i <= n; i++){
cin >> a[i];
//cout << a[i] << " ";
}
// cout << endl;
for (int i = 1; i <= n; i++){
cin >> b[i];
//cout << b[i] << " ";
f[i].x = a[i]-b[i];
f[i].y = a[i];
f[i].z = b[i];
}
// cout << endl;
int res = 0;
sort(f+1, f+n+1, cmp);
for (int i = 1; i <= n; i++){
if (i <= k) res+=f[i].y;
else{
if (f[i].x<=0) res+=f[i].y;
else res+=f[i].z;
}
}
// for (int i = 1; i <= n; i++){
// cout << f[i].z << " ";
// }
// cout << endl;
cout << res;
return 0;
}
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