#include <fstream>
using namespace std;

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

const int N=5000005;

int v[N],dq[N],st,dr,n,k,i;
long long sum;

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

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

void stanga(int i)
{
	if(i-dq[st]==k)
		++st;
}

int main()
{
	in>>n>>k;
	st=1;dr=0;
	for(i=1;i<=n;i++)
		in>>v[i];
	for(i=1;i<=k;i++)
	{
		dreapta(i);
		dq[++dr]=i;
	}
	sum+=v[dq[st]];
	for(;i<=n;i++)
	{
		stanga(i);
		dreapta(i);
		adauga(i);
		sum+=v[dq[st]];
	}
	out<<sum<<"\n";
	
	return 0;
}