#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;
    S=0;
    int i;
    int pr=1,ul=1;
    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--;
                }
                else break;
            }
        }
        while(c[pr]<i-k+1)
        {
            pr++;
        }
        if(i>=k)
        {
            S=S+v[c[pr]];
        }
    }
    fout<<S;
    fin.close();
    fout.close();
    return 0;
}