#include<fstream>
using namespace std;
int st=1,dr,dq[5000000],v[5000000],k,n;
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()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    int i;
    long long s;
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>v[i];
    for(i=1;i<=n;i++)
    {
        if(i>k)
            stanga(i);
        dreapta(i);
        if(i>=k)
            s=s+v[dq[st]];
    }
    g<<s;
    return 0;
}