#include <bits/stdc++.h>

using namespace std;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);
    int n,k;
    cin>>n>>k;
    vector<int> v(n);
    for(int i=0;i<n;i++)
    {
        cin>>v[i];
    }
    sort(v.rbegin(),v.rend());
    int pointer=0;
    int AmountLeft;
    long long ans=0;
    while(pointer<n)
    {
        ans+=2*v[pointer];
        ans+=2*min((int)v.size()-pointer,k);
        pointer+=min((int)v.size()-pointer,k);
        //cout<<ans<<"\n";
    }
    cout<<ans;
}