#include <stdio.h>
long long st,dr,i,n,k,s,v[3350000],a[5000000];
int main()
{freopen("deque.in","r",stdin);freopen("deque.out","w",stdout);
 st=1;dr=0;
 scanf("%lld%lld",&n,&k);
 for(i=1;i<=n;i++)
  {scanf("%lld",&a[i]);
   while(st<=dr&&a[v[dr]]>a[i])dr--;
   dr++;v[dr]=i;
   if(v[st]==i-k)st++;
   if(i>=k)s+=a[v[st]];
  }
 printf("%lld",s);
 fclose(stdin);fclose(stdout);
 return 0;
}