#include<fstream.h>
long n,k,i,j,x,v[100000],s=0;
long min;
ifstream f("deque.in");
ofstream g("deque.out");
int main()
{
f>>n>>k;
for (i=0;i<n;i++) f>>v[i];
for (i=0;i<n-k-1;i++)
	{
	min=10000001;
	for (j=0;j<k;j++)
		{
		x=i;
		if (min>v[x]) min=v[x];
		x++;
		}
	s+=min;
	}
cout<<s;
return 0;
}