#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000009],c[5000009],n,k;
long long S;
int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    c[1]=1;
    int i;
    int pr=1,ul=1;
    do
    {
        for(i=2;i<=n;i++)
        {
            ul++;
            c[ul]=i;
            if(v[c[ul]]<=v[c[ul-1]])
            {
                for (int j=ul; j>pr; j--)
                if(v[c[j]]<=v[c[j-1]])
                {
                    c[j-1]=c[j];
                    ul--;
                }
            }
            while(c[pr]<i-k+1)
            {
                pr++;
            }
            if(i>=k)
            {
                S=S+v[c[pr]];
            }
        }
    } while(i<n);
    fout<<S;
    fin.close();
    fout.close();
    return 0;
}