#include<fstream>
#include<iostream>
#include <stdio.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k;
long long s=0;
int deq[5000000]={0};
int main()
{
    fin>>n>>k;
    int a[n];
    for (int i=1; i<=n; i++)
        fin >> a[i];
    int inceput = 1, sfarsit = 0;

    for (int i = 1; i <= n; i++)
    {
        while (inceput <= sfarsit and A[i] <= A[deq[sfarsit]])
            sfarsit--;
        deq[++sfarsit] = i;

        if (deq[inceput] == i - k)
            inceput++;

        if (i >= k)
            s += a[deq[inceput]];
    }
    fout << s;
    fout.close();
    return 0;
}