#include <iostream>
#include <fstream>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

const int dim = 5000005;

int a[dim],dq[dim],st,dr,n,k;
long long int sum;

int main()
{
    in >> n >> k;
    st = 1;
    dr = 0;
    for (int i=1; i<=n; i++)
    {
        in >> a[i];
    }
    for (int i=1; i<=n; i++)
    {
        if (st <= dr && dq[st] == i-k)
        {
            st++;
        }

        while (st <= dr && a[i] <= a[dq[dr]])
        {
            dr--;
        }
        dq[++dr] = i;
        if (i >= k)
        {
            sum += a[dq[st]];
        }
    }
    out << sum;
    return 0;
}