#include <cstdio>
using namespace std;
int i,n,k;
int a[5000010],deq[5000010];
int front,back;
long long sum;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.in","r",stdout);
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
    scanf("%d",&a[i]);
    front=1;back=0;
    for(i=1;i<=n;i++)
    {
        while(front<=back&&a[i]<=a[deq[back]])back--;
        deq[++back]=i;
        if(deq[front]==i-k)front++;
        if(i>=k)sum+=a[deq[front]];
    }
    printf("%lld\n",sum);
    return 0;
}