#include <iostream>
#include <cstdio>

#define nmax 5000005

using namespace std;

int n, k;
int a[nmax], Deque[nmax];
long long s;

void citire()
{
    scanf("%d%d ",&n, &k);
    for (int i = 1; i <= n; i++)
        scanf("%d", &a[i]);
}

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    citire();

    int Front = 1;
    int Back = 0;

    for (int i=1; i <= n; i++)
    {

        while (Front <= Back && a[i] <= a[Deque[Back]])
            Back--;
        Deque[++Back] = i;

        if (Deque[Front] == i-k)
            Front++;
        if (i >= k)
            s += a[ Deque[Front]];
    }

    printf("%lld\n", s);

    return 0;
}