#include<iostream>
#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,p = 1,u = 0, j;
long long suma = 0;
int v[5000005],coada[5000005],pozmin;
int main()
{
    fin>>n>>k;
    for(int i = 1; i <= n; ++i)
    {
        fin>>v[i];
    }

    for(int i = 1;i <= n; ++i)
    {
        if(coada[p] == i-k)
        {
            p++;
        }
        if(u < p)
        {
            u = p;
            coada[p] = i;
        }
        else
        {
            j = p;
            while(v[coada[j]] < v[i] and j <= u)
            {
                j++;
            }
            coada[j] = i;
            u = j;
        }
        if(i >= k)
        {
            suma += v[coada[p]];
        }
    }
    fout<<suma;
}