#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

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

long long n, k, suma, q;
vector <int> a, m;

int main()
{
    int n;
    cin >> n >> k;
    a.resize(n);

    for (int i = 0; i < k; cin >> a[i++] );
    suma = q = *(min_element(a.begin(), a.begin() + k));

    m.push_back(suma);
    for (int i = k; i < a.size(); i++)
    {
        cin >> a[i];
        if (a[i] < q) q = a[i];
        if (a[i - k] == q) q = *(min_element(a.begin() + i - k + 1, a.begin() + i + 1));
        suma += q;
        m.push_back(q);
    }

    cout << suma;

    return 0;
}