#include <cstdio>
#include <deque>
using namespace std;
 
int main()
{
   freopen("deque.in","r",stdin);
   freopen("deque.out","w",stdout);
   int n,k;
   scanf("%d%d",&n,&k);
   long long sum=0;
   deque<int>d;
   deque<int>poz;
   for(register int i=1;i<=n;i++)
   {
       int nr;
       scanf("%d",&nr);
       if(i<k)
       {
        while(!d.empty())
       {
          if(d.back()>=nr)d.pop_back(),poz.pop_back();
          else
            break;
       }
       d.push_back(nr);
       poz.push_back(i);
       continue;
       }
       if(i>=k)
       {
                while(!d.empty())
       {
          if(d.back()>=nr)d.pop_back(),poz.pop_back();
          else
            break;
       }
       d.push_back(nr);
       poz.push_back(i);
        sum+=d.front();
        if(poz.front()==(i-k+1))
            d.pop_front(),poz.pop_front();
       }
   }
   printf("%lld",sum);
    return 0;
}