#include <iostream>
#include <deque>
#include <fstream>
#include <queue>
#define int long long
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
priority_queue<struct elem> q;


struct elem
{
    int nr,poz;
    bool operator < (const elem other)const
    {
        return nr>other.nr;
    }
};




signed main()
{
    int n,k,x,ct=0,s=0;
    fin>>n>>k;
    for(int i=1;i<=k;i++)
    {
        fin>>x;
        q.push({x,i});
    }
    s=s+q.top().nr;
    ct=k;
    while(ct<n)
    {
        ct++;
        fin>>x;

        //cout<<x<<" ";
        q.push({x,ct});
        while(ct-q.top().poz>=k )
        {
                q.pop();
        }
        s=s+q.top().nr;
    }


    fout<<s;

}