#include<cstdio>
#define N 5000000
long long s,n,v[N],u,p,k;
long long d[N];
void citire()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%lld%lld",&n,&k);
	for (int i=1; i<=k; ++i)
	{
		scanf("%lld",&v[i]);
		while (v[i]<=v[d[u-1]]&&u!=p)
			--u;
		d[u++]=i;
	}
	s+=v[d[p]];
	for (int i=k+1; i<=n; ++i)
	{
		scanf("%lld",&v[i]);
		int g=i-d[p];
		if (g==k)
			++p;
		while (u!=p&&v[i]<=v[d[u-1]])
			--u;
		d[u++]=i;
		s+=v[d[p]];
	}
	printf("%lld",s);
}
int main()
{
	citire();
	return 0;
}