#include <iostream>
#include <fstream>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

long long n, k, i, suma, x, dFront, dBack, dSize;

int main()
{
    in >> n >> k;
    pair<long long, long long> deq[2 * k + 2];
    dFront = k;
    dBack = k + 1;
    dSize = 0;


    for(i = 1; i <= k; i++)
    {
        in>>x;

        while(dSize > 0 && deq[dBack].first >= x)
        {
            dBack++;
            dSize--;
        }

        dBack--;
        dSize++;
        deq[dBack] = make_pair(x, i);
    }

    suma = deq[dFront].first;

    for(i = k + 1; i <= n; i++)
    {
        in>>x;
        while(dSize > 0 && i - deq[dFront].second >= k)
        {
            dFront--;
            dSize--;
        }

        while(dSize > 0 && deq[dBack].first >= x)
            {
                dBack++;
                dSize--;
            }

        dBack--;
        dSize++;
        deq[dBack] = make_pair(x, i);

        suma += deq[dFront].first;
    }

    out<<suma;

    return 0;
}