#include <iostream>
#include <fstream>
using namespace std;

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

int n, k;
int a[5000001], d[5000001];
int p, u;
long long int suma = 0;

int main()
{
    f >> n >> k;
    for (int i = 1; i <= n; i++)
        f >> a[i];
    p = 1; u = 0;

    for (int i = 1; i <= n; i++) {
        while (p <= u && a[i] <= a[d[u]])
            u--;
        d[++u] = i;
        if (d[p] == i - k) p++;
        if (i >= k) suma += a[d[p]];
    }

    g << suma;
    return 0;
}