#include <iostream>
#include <fstream>
#define N 5000001

using namespace std;

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

int arr[N], deque[N];

int main()
{
    int n, k;
    long long sum = 0;
    int front, back;

    fin >> n >> k;

    for (int i = 1; i <= n; ++i)
        fin >> arr[i];

    fin.close();

    front = 1;
    back = 0;

    for (int i = 1; i <= n; ++i)
    {
        while (front <= back && arr[deque[back]] >= arr[i]) --back;
        deque[++back] = i;

        if (i - k == deque[front]) ++front;
        if (i >= k) sum += arr[deque[front]];
    }

    fout << sum;
    fout.close();

    return 0;
}