#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

int main() {
	int n, subsir;
	long long s = 0;
	in >> n >> subsir;
	deque<int> d(n);
	for (int i{}; i < n; ++i) {
		in >> d[i];
	}
	while (d.size() >= subsir){
		int min = 10000000;
		for (int i{}; i < subsir; ++i) {
			int x = *(d.begin() + i);
			if (x < min) {
				min = x;
			}
		}
		s += min;
		d.pop_front();
	}
	out << s;
}