#include <bits/stdc++.h>
#define int long long
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define tam(x) (int)(x).size()
#define endl '\n'
#define sd second
#define fs first
#define maxs(x,y) (x = max(x,y))
#define mins(x,y) (x = min(x,y))
#define optmizar_io ios_base::sync_with_stdio(0); cin.tie(0);
#define Setpre(n) cout << fixed <<setprecision(n)
#define dbg(x) for(auto y: x) cout << y <<' '; cout << endl;
#define dbg1(x) for(auto y: x) cout << y.first <<' '<< y.second << endl;
#define dbg2(v) for(auto x: v) cout << x.a<< ' '<< x.b <<' '<< x.c << endl;
const int MAX = 501;
const int INF = 1e17;
const int Mod = 1e9+7;
const int zero = 0;
const double eps = 1e-6;
const double PI=acos(-1.0);
const int mox[8] ={-1,1,0,0,-1,-1,1,1};
const int moy[8] ={0,0,-1,1,-1,1,-1,1};
using namespace std;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pi;
typedef vector<bool> vbol;
typedef array<int, 3> arr;
void cases(string s){
#ifndef ONLINE_JUDGE
if(tam(s) == 0) s = "1";
string a = s + ".in";
string b = s + ".out";
freopen(a.c_str(), "r", stdin);
freopen(b.c_str(), "w", stdout);
#endif
}
void _1()
{
int n, m; cin >> n >> m;
vi ar1(n), ar2(n);
for(int &x : ar1) cin >> x;
for(int &x : ar2) cin >> x;
priority_queue<pi, vector<pi>, greater<pi> > pq;
for(int i = 0; i < n; i++) pq.push({0 , i});
for(int i = 0; i < n; i++)
{
for(int j = 0; j < m; j++)
{
auto [a, b] = pq.top(); pq.pop(); pq.push({a + ar1[b], b});
}
}
int mini = INF;
while(tam(pq))
{
//cout << pq.top() << " ";
mins(mini, pq.top().first); pq.pop();
}
cout << mini << endl;
}
int32_t main() {
optmizar_io
// cases("");
//start:
//end:
//tags:
//difficulty:
//comment:
int T = 1; //cin >> T;
while(T--)
_1();
return 0;
}
