#include <fstream>
using namespace std;
int v[5000000];

int main() {
	ifstream fin("deque.in");
	ofstream fout("deque.out");
	int n, k;
	fin >> n >> k;
	for (int i = 0; i < n; ++i) {
		fin >> v[i];
	}
	long long sum = 0;
	for (int i = 0; i < n - k + 1; ++i) {
		int min_val = 10000001;
		for (int j = i; j < i + k; ++j) {
			if (min_val > v[j]) {
				min_val = v[j];
			}
		}
		sum += min_val;
	}
	fout << sum;
	return 0;
}