#include <bits/stdc++.h>

using namespace std;
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int const maxn = 5e6 + 7;
long long const mod = 1000000007;
int n, m, cnt[maxn];
priority_queue<int> q;
vector<int> noize, cost;

void input() {
    cin >> n >> m;
    int temp;
    for (int i = 0; i < n; i++) {
        cin >> temp;
        noize.push_back(temp);
    }
    for (int i = 0; i < n; i++) {
        cin >> temp;
        cost.push_back(temp);
    }
}

void solve() {
    long long ans = mod * mod;
    for (int i = 0; i <= n - m; i++) {
        int currmin = mod;
        long long currans = 0;
        for (int j = i; j < i + m; j++) {
            currmin = min(currmin, noize[j]);
        }
        for (int j = i; j < i + m; j++) {
            currans += cost[j] * (noize[j] - currmin);
        }
        ans = min(ans, currans);
    }
    cout << ans;
}

int32_t main() {
    IOS
    input();
    solve();
    return 0;

}