#include<stdio.h>
#include<stdlib.h>
#define MAXN 5000000

long a[MAXN],d[MAXN],n,k,i,p=1,u=0;
long long s=0;

int main() {
  freopen("deque.in","r",stdin);
  scanf("%d%d",&n,&k);
  for(i=0;i<n;i++) scanf("%d",a+i);
  fclose(stdin);
  for(i=0;i<n;i++) {
    while((u>=p)&&(a[d[u]]>=a[i])) u--;
    d[++u]=i;
    if(i>=k-1) {
      if(d[p]==i-k+1) p++;
      s+=a[d[p]];
    }
  }
  freopen("deque.out","w",stdout);
  printf("%lld",s);
  fclose(stdout);
  return 0;
}