#include <fstream>
#pragma GCC optimiza("Ofast")

using namespace std;

int v[5000001];

struct q
{
    int indice;
    int val;
};

q coada[5000001];

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n,i,l,r,j,k,b;
    long long s;
    fin >> n >> k;
    for (i=1; i<=n; i++)
        fin >> v[i];
    l=1;
    j=0;
    coada[0].val=-10000001;
    s=0;
    for (i=1; i<=n; i++)
    {
        while (v[i]<=coada[j].val && coada[j].indice>=i-k+1)
        {
            j--;
        }
        j++;
        coada[j].val=v[i];
        coada[j].indice=i;
        if (i>=k)
        {
            if (coada[l].indice<i-k+1)
                l++;
            s+=coada[l].val;
        }
    }
    fout << s;
    return 0;
}