#include<iostream>
#include<conio.h>
#include<fstream>
using namespace std;
#define max 5000010
int N,K,in,sf;
int A[max],deque[max];
long long Sum;
int main()
{
	ifstream f("deque.in");
	ofstream g("deque.out");
	f>>N>>K;
	int i;
	for(i=1;i<=N;i++)
		f>>A[i];
	in=1; sf=0;
	for(i=1;i<=N;i++)
	{
		while(in<=sf&&A[i]<A[deque[sf]]) sf--;
		deque[++sf]=i;
		if(deque[in]==i-K) in++;
		if(i>=K) Sum=Sum+A[deque[in]];
	}
	g<<Sum;
	f.close();
	g.close();
	getch();
	return 0;
}