#include<fstream>
#include<algorithm>
#define nmax 5000005
#define inf 100000000
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,a[nmax],minim=-inf,ant_minim=-inf;
long long s;
int main()
{
	int i;
	f>>n>>k;
	for(i=0;i<n;i++)
		f>>a[i];
	i=0;
	while(i+k<=n)
	{
		int j;
		minim=a[i];
		for(j=i+1;j<i+k;j++)
		{
			minim=min(a[j],minim);
			ant_minim=minim;
		}
		s+=minim;
		i++;
	}
	g<<s<<'\n';
	f.close();
	g.close();
	return 0;
}