#include <fstream>

using namespace std;

int t[5000003],k,dq[5000003],i,j,m,n,p,u;

ifstream fin("deque.in");
ofstream fout("deque.out");

void adauga(int poz)
{
    if (i>=k && dq[p]==i-k) p++;
    while (u>=p && t[dq[u]]>t[poz]) u--;
    u++;
    dq[u]=poz;
}

int main()
{
    long long sum=0;
    fin>>n>>k;
    for (i=1;i<=n;i++)
        fin>>t[i];
    p=1;
    u=0;
    for (i=1;i<=k;i++)
        adauga(i);
    sum+=t[dq[p]];
    //fout<<t[dq[p]]<<"\n";
    for (i=k+1;i<=n;i++)
    {
        adauga(i);
        sum+=t[dq[p]];
        //fout<<t[dq[p]]<<"\n";
    }
    fout<<sum;
    return 0;
}