#include<fstream>
using namespace std;
const int N=5000005;
int v[N], d[N], st,dr,n,i,k;
long long int s;
ifstream in("deque.in");
ofstream out("deque.out");
inline void dreapta(int i)
{ 
	while (st<=dr && v[d[dr]]>=v[i])--dr;
}
inline void stanga (int i)
{
	if(i-d[st]==k)++st;
}
inline void adauga(int i)
{
	d[++dr]=i;
}
int main ()
{
	in>>n>>k;
	for(i=1;i<=n;++i)in>>v[i];
	dr=-1;
	for(i=1;i<=k;++i)
	{
		dreapta(i);
		adauga(i);
	}
	s=v[d[st]];
	for(i=k+1;i<=n;++i)
	{
		stanga(i);
		dreapta(i);
		adauga(i);
		s+=v[d[st]];
	}	
	out<<s;
}