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

            d[++back]=i;

            if (d[front]==i-k) front ++;

            if (i>=k) sum+= a[d[front]];

        }
    g<<sum;
    g.close();

    return 0;
}