#include<cstdio>
using namespace std;

int deque[5000001], a[5000001], front, back, n, k;
long long suma;
void citire()
{
    int i;
    scanf("%d",&n,&k);
    for(i=1;i<=n;i++)
        scanf("%d",&a[i]);
}
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    citire();
    int i;
    front=1;
    back=0;
    for(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)suma+=a[deque[front]];
    }
    printf("%d\n",suma);
    return 0;
}