#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pi pair<int, int>
#define vi vector<int>
#define vs vector<string>
#define vb vector<bool>
#define vpi vector<pi>
#define pb push_back
#define all(a) (a).begin(), (a).end()
const int mod = 1e9 + 7;
void solve()
{
int n, m;
cin >> n >> m;
int a[n], b[n], cnt[n];
multiset<pi> ms;
for (int i = 0; i < n; i++)
{
cin >> a[i];
cnt[i] = 0;
ms.insert({0, i});
}
for (int i = 0; i < n; i++)
{
cin >> b[i];
}
for (int i = 1; i <= (n * m); i++)
{
auto p = *ms.begin();
ms.erase(ms.begin());
if (cnt[p.second] == m)
{
ms.insert({p.first + b[p.second], p.second});
}
else
{
if (a[p.second] > b[p.second])
{
ms.insert({p.first + a[p.second], p.second});
cnt[p.second]++;
}
else
{
ms.insert({p.first + b[p.second], p.second});
}
}
}
cout << ms.begin()->first << '\n';
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(NULL);
cout.tie(NULL);
int t = 1;
// cin >> t;
while (t--)
{
solve();
}
return 0;
}
