#include<stdio.h>
#define NMAX 5000001
int c[NMAX],pr,ul,a[NMAX],n,k;
long sum;
int main()
{
	int i;
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d%d",&n,&k);
	for(i=1;i<=n;i++)
		scanf("%d",&a[i]);
	pr=1;
	for(i=1;i<=n;i++)
	{
		for(;pr<=ul&&a[i]<=a[c[ul]];--ul);
		c[++ul]=i;
		if(c[pr]==i-k)
			pr++;
		if(i>=k)
			sum+=a[c[pr]];
	}
	printf("%ld",sum);
	return 0;
}