#include<stdio.h>

int a[5000001],i,b[5000001],s,d,n,k,;
long long sum;

int main()
{ freopen("deque.in","r",stdin);
  freopen("deque.out","w",stdout); 
  
  scanf("%d %d",&n,&k);
   s=1;
   d=0;
   for(i=1;i<=n;i++) { scanf("%d",&a[i]);
                       while(d>=s&&a[i]<b[d]) { b[d]=0;
                                                --d;
                                              }
                       d++;
                       b[d]=a[i];
                       if(i>=3)  sum+=b[s];
                       if(b[s]==a[i-k+1]) s++;
                     }
   printf("%d\n",sum);
   fclose(stdin);
   fclose(stdout);
   return 0;
}