#include <bits/stdc++.h>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");
int v[5000001];
int dequee[5000001];
int main()
{
    int n, k;
    
    in >> n >> k;
    
    long int suma = 0;

    for (int i = 1; i <= n; i++)
    {
        in >> v[i];
    }
    int front = 1, back = 0;
	for (int i = 1; i <= n; i++)
    {   
        while(front <= back && v[i]<=v[dequee[back]])
            back--;

        back++;
        dequee[back]=i;
        if (dequee[front] == i-k) front++;

        if (i >= k) suma += v[dequee[front]]; 
    }

    out << suma;
	return 0;
}