#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000005], n, k, minim = 1, sum;

int main() {
	fin >> n >> k;
	for (int i = 1; i <= n; ++i)
		fin >> v[i];
	for (int i = 2, j = 1; i <= n; ++i) {
		if (v[i] < v[minim])
			minim = i;
		if (i == j + k - 1) {
			sum += v[minim];
			++j;
			i = i - k + 2;
			minim = i;
		}
	}
	fout << sum;
	return 0;
}