#include <fstream>
#define NMAX 5000000

using namespace std;

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

int n, k, A[NMAX], Deque[NMAX], st = 0, dr = -1;
long long sum;

int main()
{
    in >> n >> k;

    for (int i = 1; i <= n; i++)
    {
        in >> A[i];

        while (st <= dr && A[i] <= A[ Deque[dr] ])
            dr--;

        Deque[++dr] = i;

        if (Deque[st] == i - k)
            st++;

        if (i >= k)
            sum += A[Deque[st]];
    }

    out << sum;
    return 0;
}