#include <bits/stdc++.h>
using namespace std;
 
#define ll long long
#define mset(arr,x) memset(arr,x,sizeof(arr))
#define rep(i,s,e) for(i=s;i<=e;i++)
#define rrep(i,s,e) for(i=s;i>=e;i--)
#define min(a,b) ((a)<(b)?(a):(b))
#define max(a,b) ((a)>(b)?(a):(b))
#define pb push_back
#define mp make_pair
#define f first
#define s second
#define all(c) c.begin(),c.end()
 
vector< pair<ll ,ll> > vc;
ll arr[2000010], barr[2000010];
bool comp( pair<ll ,ll> pa1, pair<ll ,ll> pa2 )
{
    return (pa1.f-pa1.s)<(pa2.f-pa2.s);
}
int main()
{
     ios_base::sync_with_stdio(false);
     cin.tie(0);
 
     ll T, N, K, i, j, ans = 0;
     string st;
 
     cin >> N >> K;
     rep(i, 1, N)
     {
         cin >> arr[i];
     }
     rep(i, 1, N)
     {
         cin >> barr[i];
         vc.pb( mp(arr[i], barr[i]) );
     }
     sort( all(vc), comp );
     rep(i, 0, K-1)
     {
         ans += vc[i].f;
     }
     rep(i, K, N-1)
     {
         if( vc[i].f<vc[i].s )
         {
             ans += vc[i].f;
         }
         else
         {
             ans += vc[i].s;
         }
     }
     cout << ans;
 
     return 0;
}