#include <stdio.h>
#define NMAX 5000005
#define ll long long
int n,k,A[NMAX],deq[NMAX],inc,sf;
ll sum;
void read()
{
	scanf("%d%d",&n,&k);
	int i;
	for (i=1; i<=n; i++)
		scanf("%d",&A[i]);
}
void actualizare(int i)
{
	while (inc!=sf && A[deq[sf-1]]>=A[i])
		sf--;
	deq[sf++]=i;
}
void capat_st(int i)
{
	if (i-deq[inc]>=k)
		inc++;
}
void solve()
{
	int i;
	for (i=1; i<=n; i++)
	{
		actualizare(i);
		capat_st(i);
		if (i>=k)
			sum+=A[deq[inc]];
	}
}
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	read();
	solve();
	printf("%lld\n",sum);
	return 0;
}