#include <fstream>
#include <vector>
#include <algorithm>
#include <set>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
multiset <int> s;
int v[5000005];
int main()
{
	int n, k;
	cin >> n >> k;
	int x;
	for (int i = 1; i <= n; i++)
		cin >> v[i];
	int sum = 0;
	for (int i = 1; i <= k; i++)
		s.insert(v[i]);
	for (int i = k+1; i <= n; i++)
	{
		sum += *s.begin();
		s.erase(v[i - k]);
		s.insert(v[i]);
	}
	sum += *s.begin();
	cout << sum;
}