#include <iostream>
#define MAXIM 5000000
using namespace std;

int main(void)
{
    long long suma = 0;
	int n, k;
    cin >> n >> k;
    int *a;
    a = new int[MAXIM];
    if (a == NULL) {
        cout << "Error";
        return -1;
    }
    int *Deque;
    Deque = new int[MAXIM];
    if (Deque == NULL) {
        cout << "Error";
        return -1;
    }
    int st = 1, dr = 0;
    for (int i = 0; i < n; i++)
        cin >> a[i];
    for (int i = 0; i < n; i++) {
        while (st <= dr && a[i] <= a[Deque[dr]])
            dr--;    
        Deque[++dr] = i;
        if (Deque[st] == i - k)
            st++;
        if (i >= k - 1)
            suma += a[Deque[st]];
    }
    delete[] a;
    delete[] Deque;
    cout << suma;
	return 0;
}