#include<fstream>
using namespace std;

int i,n,k,x,st,d[5000009],m,dr=0,a[5000009];
long long s=0;
int main()
{
	ifstream f("deque.in");
	ofstream g("deque.out");
	f>>n>>k;
	for(i=1;i<=n;i++)
		f>>a[i];
	st=1;
	for(i=1;i<=n;i++)
	{
		while(st<=dr&&a[i]<a[d[dr]])
			dr--;
		d[++dr]=i;
		if(d[st]==i-k)
			st++;
		if(i>=k)
			s+=a[d[st]];
	}
	g<<s;
	return 0;
}