#include <iostream>
#include <fstream>

using namespace std;

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

int v[5000001];
int n, k, i, l, r;
long long s;
int *deq = new int[5000001];

int main()
{

    f>>n>>k;
    for (i = 1; i <= n; i++)
        f>>v[i];

    l = 1;
    r = 0;                   //deque-ul este vid

    for (i = 1; i <= n; i++)
    {
        while (l <= r && v[i] <= v[ deq[r] ])
            r--;

        deq[++r] = i;
        if (deq[l] == i-k) l++;
        if (i >= k)
            s += v[ deq[l]];
    }

    delete[] deq;
    g<<s;

    return 0;
}