#include <iostream>
#include <fstream>
using namespace std;
int a[5000000], deq[5000000];
int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int N, k, front = 0, back = -1;
    long long sum = 0;
    fin>>N>>k;
    for (int i = 0; i < N; i++)
        fin>>a[i];
    for (int i = 0; i < N; i++)
    {
        while (front <= back && a[i] <= a[deq[back]])
        {
            back--;
        }
        deq[++back] = i;
        if (deq[front] == i - k)
            front++;
        if (i >= k-1)
            sum += a[deq[front]];
    }
    fout<<sum;
    fin.close();
    fout.close();

}