#include<stdio.h>
long n,k,i,x,st,dr,q[5000000],s;
void rez()
{
	scanf("%ld %ld",&n,&k);
	for(i=1;i<=k;++i)
	{
		scanf("%ld",&x);
		while(x<q[dr] && i!=1) dr--;
		q[++dr]=x;
	}
	st=1;
	for(i=k+1;i<=n;++i)
	{
		scanf("%ld",&x);
		s+=q[st];
		st++;
		while(x<q[dr]) dr--;
		q[++dr]=x;
	}
	printf("%ld\n",&s);
}
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	rez();
	return 0;
}