#include <fstream>
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
int st, dr, dq[5000001], k, n, v[5000001];
void stanga(int i)
{
    if(i-dq[st]==k)
        st++;
}
void dreapta (int i)
{
    while (st<=dr && v[i]<=v[dq[dr]])
        dr--;
    dq[++dr]=i;
}
int main()
{
    int N, i;
    long long s = 0;
    fin>>N>>k;
    for(i=1; i<=N; i++)
    {
        fin>>v[i];
        dq[i]=v[i];
    }
    st=1;
    dr=0;
    for(i=1; i<=N; i++)
    {
        if(i>k)stanga(i);
        dreapta(i);
        if(i>=k) s+=v[dq[st]];
    }
    fout<<s;
    return 0;
}