#include<stdio.h>
int k, n, a[10000005], de[10000005], i, f, b;
long long sum;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d %d",&n,&k);
    for(i=1;i<=n;i++)
        scanf("%d",&a[i]);
    f=1;
    for(i=1;i<=n;i++)
    {
        while(f<=b && a[i]<=a[de[b]]) b--;
        de[++b]=i;
        if(de[f]==(i-k))
            f++;
        if(i>=k)
            sum+=a[de[f]];
    }
    printf("%lld ",sum);
    return 0;
}