#include <fstream>

using namespace std;

int main()
{
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    int n,k,d[50000],v[50000],p=1,u=1;
    long long int rez=0;
    fin>>n>>k;
    for (int i=1;i<=n;i++)
        fin>>v[i];
    d[u]=1;
    for (int i=2;i<=n;i++)
        {
        while (v[d[u]]>=v[i]&&u>=p)
            u--;
        u++;
        d[u]=i;
        if (d[p]<=i-k)
            p++;
        if (i>=k)
            rez=rez+v[d[p]];
        }
    fout<<rez;
    fin.close();
    fout.close();
    return 0;
}