#include<fstream>
using namespace std;

const int N = 5000001;

int d[N],v[N];
int st,dr,n,i,k;
long long s;
inline void stanga(int i)
{
	if(i-d[st]==k)
		++st;
}

inline void dreapta(int i)
{
	while(st<=dr&&v[d[dr]]>=v[i])
	{
		--dr;
	}
}

inline void adauga(int i)
{
	d[++dr]=i;
}


ifstream in("deque.in");
ofstream out("deque.out");

int main()
{
	st=1;
	dr=0;
	in>>n>>k;
	
	for(i=1;i<=n;++i)
		in>>v[i];
	
	for(i=1;i<=k;++i)
	{
		dreapta(i);
		adauga(i);
	}
	s+=v[d[st]];
	for(;i<=n;++i)
	{
		stanga(i);
		dreapta(i);
		adauga(i);
		s+=v[d[st]];
	}
	
	out<<s;
}