#include<stdio.h>

int a[5000010],i,b[5000010],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]);
   for(i=1;i<=n;i++) { while(d>=s&&a[i]<a[b[d]]) --d;
                                              
                       d++;
                       b[d]=i;
                       if(i>=k) sum+=a[b[s]];
                       if(b[s]==i-k+1) s++;
                     }
   printf("%lld\n",sum);
   fclose(stdin);
   fclose(stdout);
   return 0;
}