#include <bits/stdc++.h>
using namespace std;
#define all(x) x.begin(), x.end()
// #define int long long
int solve()
{
    int n;
    int m;
    cin >> n >> m;
    vector<int> a(n + 2);
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i];
    }
    a[0] = a[n];
    a[n + 1] = a[1];
    vector<int> b;
    for (int i = 1; i <= n; i++)
    {
        b.emplace_back(a[i] + a[i - 1] + a[i + 1]);
    }
    sort(all(b), greater<int>());
    int ans = (n - m) * 3;
    for (int i = 0; i < m; i++)
    {
        ans += b[i];
    }
    cout << ans << "\n";

    return 0;
}
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int test = 1;
    // cin >> test;
    while (test--)
    {
        solve();
    }

    return 0;
}