#include <fstream>
#include <iostream>
constexpr auto sec = 2;

using namespace std;

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


int n, k, x, last = -1, start, deque[5000000][2];
long long Sum;

int main()
{

    f >> n >> k;

    for (int i = 0; i < k - 1; i++) {
        f >> x;

        while (last > 0 && deque[last][0] >= x) {
            last--;
        }

        deque[++last][0] = x;
        deque[last][1] = i;

    }
    for (int i = k - 1; i < n; i++) {
        f >> x;

        while (last > 0 && deque[last][0] >= x) {
            last--;
        }

        deque[++last][0] = x;
        deque[last][1] = i;


        while (deque[start][1] <= i - k) {
            start++;
        }

        Sum += deque[start][0];
    }
    g << Sum;
}