#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int deque[5000001], a[5000001], front, back, n, k;
long long suma;
void citire()
{
    int i;
    f>>n>>k;
    for(i=1;i<=n;i++)f>>a[i];
}
int main()
{
    citire();
    int i;
    front=1;
    back=0;
    for(i=1;i<=n;i++)
    {
        while(front<=back&&a[i]<=a[deque[back]])back--;
        deque[++back]=i;
        if(deque[front]==i-k)front++;
        if(i>=k)suma+=a[deque[front]];
    }
    g<<suma;
    f.close();
    g.close();
    return 0;
}