#include<fstream.h>
int n,k,v[5000001],a[5000001];
long long s;
ifstream f("deque.in");
ofstream g("deque.out");
int main()
{
int i,p,u;
f>>n>>k;
for (i=1;i<=n;i++) f>>v[i];
p=1;
u=0;
for (i=1;i<=n;i++)
	{
	while (p<=u&&v[i]<=v[a[u]]) u--;
	a[++u]=i;
	if (a[p]==i-k) p++;
	if (i>=k) s+=v[a[p]];
	}
/*for (i=0;i<n-k+1;i++)
	{
	min=5001;
	for (j=i;j<i+k;j++)
		if (min>v[j]) min=v[j];
	s+=min;
	}*/
g<<s;
g.close();
return 0;
}