#include <fstream>
#include <deque>

using namespace std;

void solve();

int a[5000005];

int main()
{
	solve();
	return 0;
}

void solve()
{
	ifstream fin("deque.in");
	ofstream fout("deque.out");
	int n,k;
	long long int sum = 0;
	deque<int> q;
	fin>>n>>k;
	for(int i=1;i<=n;i++)
	{
		fin>>a[i];
		while(!q.empty() && a[i] <= a[q.back()])
		{
			q.pop_back();
		}
		q.push_back(i);
		if(i - q.front() >= k)
		{
			q.pop_front();
		}
		if(i >= k) 
		{
			sum += a[q.front()];
		}
	}
	fout<<sum;
}