#include<stdio.h>
#include<vector>
#include<algorithm>
#include<deque>
using namespace std;

// just chilling ( e admiterea la unibuc maine :p, si nu am mai codat de mult.. )

#define NMAX 5000005
int A[NMAX],D[NMAX];

int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	
	int N,K;
	
	scanf("%d%d",&N,&K);
	
	int i;
	for(i=1; i<=N; ++i)
		scanf("%d",&A[i]);
	
	long long ANS=0;
	
	int inc=1,sf=0;
	
	A[0]=-90000009;
	
	for(i=1; i<=N; ++i)
	{
		if( A[i]<=A[D[inc]] ) sf=inc-1;
		else
			while( A[i]<=A[D[sf]] && sf>=inc )--sf;
		
		D[++sf]=i;
		
		int old=i-K+1;
		while( D[inc]<old ) ++inc; 
	
		if( i>=K )
			ANS+=A[ D[inc] ];
	}
	
	printf("%lld\n",ANS);
	
	return 0;
}