#include <fstream>
#include <deque>

using namespace std;

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

#define MaxN 5000001
#define LL long long 

int n, k;
LL s;
deque<int> deq;
int a[MaxN];


int main()
{
	fin >> n >> k;

	for (int i = 1; i <= n; ++i)
		fin >> a[i];
	
	for (int i = 1; i <= n; ++i)
	{
		while (!deq.empty() && a[i] <= a[deq.back()])
			deq.pop_back();

		deq.push_back(i);

		if ( deq.front() == i - k ) 
			deq.pop_front();

		if ( i - k >= 0 ) 
			s += a[deq.front()];

	}

	fout << s << '\n';

	fin.close();
	fout.close();
	return 0;
}