#include<stdio.h>
using namespace std;
#define nmax 5000005
int a[nmax], dq[nmax], st, n;
long long sum;
int k;
int t;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    st = 1;
    t = 1;
    scanf("%d %d",&n,&k);
    for(int i = 1; i <= n; i++)
     scanf("%d",&a[i]);
    dq[1] = a[1];
    for(int i = 2; i <= n; i++)
      {
          while (a[i] < dq[t] && t >= st)
           t--;
         dq[++t] = a[i];
         if (i > k && dq[st] == a[i-k]) st++;
         if (i >= k) sum += dq[st];
      }
    printf("%lld",sum);
    return 0;
}