#include<fstream>
#include<queue>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque<int> dq;
long long sum;
int a[500001];
int main()
{
	int n, k, i;
	fin >> n >> k;
	for ( i = 1; i <= n; i++ )
	{
		fin >> a[i];
	}
	for ( i = 1; i <= n; i++ )
	{
		while ( !dq.empty() && a[i] <= a[dq.back()] )
			dq.pop_back();
		dq.push_back(i);
		if ( i-k == dq.front() )
		{
			dq.pop_front();
		}
		if ( i >= k )
		{
			sum += a[dq.front()];
		}
	}
	fout << sum;
	fin.close();
	fout.close();
	return 0;
}