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

ll n,k;
ll a[110000],b[110000],c[110000];
ll ans;

bool cmp(ll aa,ll bb){
    return aa>bb;
}

int main(){
    freopen("sale.in","r",stdin);
    freopen("sale.out","w",stdout);
    ios::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    cin>>n;
    for (int i=1;i<=n;i++){
        cin>>a[i];
    }
    for (int i=1;i<=n;i++){
        cin>>b[i];
    }
    cin>>k;
    for (int i=1;i<=n;i++){
        ans+=a[i];
        c[i]=b[i]-a[i];
    }
    sort(c+1,c+n+1,cmp);
    for (int i=1;i<=(n-k);i++){
        ans+=c[i];
    }
    cout<<ans<<'\n';
    return 0;
}