#include <iostream>
#include <deque>
#include <cstdio>


using namespace std;

int n, k;
int suma;
deque<int> mydeque;
void read()
{
    scanf("%d %d", &n, &k);
    int c;
    for(int i=1; i<=n; i++)
    {
        cin>>c;

        if(i%k==0)
        {
            suma += mydeque.front();
            mydeque.pop_front();
        }
        else
        {
            if(!mydeque.empty())
                while(c<mydeque.back())
                {
                    mydeque.pop_back();
                }

            mydeque.push_back(c);
        }
    }
}

int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    read();
    cout<<suma;
}