#include <fstream>
#define DIM 5000001

using namespace std;

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

long long v[DIM], deque[DIM];

int main()
{
    long long n, k;
    fin >> n >> k;
    for (int i = 1; i <= n; i++)
        fin >> v[i];

    deque[1] = 1;
    long long p = 1, u = 1;
    long long sum = 0;
    for (int i = 2; i <= n; i++)
    {
        while (p <= u && v[i] <= v[deque[u]])
            u--;
        deque[++u] = i;

        if (i - deque[p] == k)
            p++;
        if (i >= k)
            sum += v[deque[p]];
    }
    fout << sum;

    return 0;
}