#include <cstdio>

using namespace std;
# define N 5000010
int n,k,a[N],deque[N];
long long suma;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);

    scanf("%d %d",&n,&k);
    for(int i=1;i<=n;i++)
        scanf("%d",&a[i]);
    int fata=1,spate=0;
    for(int i=1;i<=n;i++)
    {
        while(fata<=spate && a[i]<=a[deque[spate]])
            spate--;
        deque[++spate]=i;
        if(deque[fata]==i-k)
            fata++;
        if(i>=k)
            suma+=a[deque[fata]];
    }
    printf("%d\n",suma);
    return 0;
}