#include<cstdio>
#include<algorithm>
#define nmax 5000005
using namespace std;
int n,k,a[nmax],d[nmax],f,b;
long long s;
int main()
{
	int i,j;
	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]);
	for(i=1;i<=n;i++)
	{
		while(f<=b && a[i]<=a[d[b]])
			b--;
		d[++b]=i;
		if(d[f]==i-k)
			f++;
		if(i>=k)
			s+=a[d[f]];
	}
	printf("%lld\n",s);
	return 0;
}