#include <iostream>
#include <fstream>
#include <deque>
#include <algorithm>
using namespace std;

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

int main()
{
	int n, k, idx = 0;
	int sum = 0;
	fin >> n >> k;
	int* a = new int[n];

	while (!fin.eof()) {
		int x;
		fin >> x;
		a[idx++] = x;
	}

	for (int i = 0; i < n - k+1; i++)
	{
		int min = a[i];
		for (int j = i+1; j < i + k; j++)
		{
			if (min > a[j])
				min = a[j];
		}
		sum += min;
	}

	fout << sum;
	return 0;

}