#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    ifstream f1("deque.in");
    ofstream f2("deque.out");

    int N, K;
    f1 >> N >> K;

    int A[N], S = 0, d[N], front = 0, back = 0;

    for (int i = 0; i < N; i++)
    {
        f1 >> A[i];

        /// remove elements from the back of the deque that are greater than or equal to A[i]
        while (back > front && A[d[back-1]] >= A[i])
        {
            back--;
        }

        /// add the current index to the back of the deque
        d[back++] = i;

        /// if the front index of the deque is i-K, move the front index forward
        if (d[front]==i-K)
            front++;

        /// if we have a sequence of size K, add the value at the front index of the deque to S
        if (i >= K)
            S += A[d[front]];
    }

    f2 << S;

    f1.close();
    f2.close();
    return 0;
}