#include<cstdio>
int n,k,i,st,dr;
int a[5000001],deque[5000001];
long long rez;
int main()
{
	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]);
	st=1;dr=0;
	for(i=1;i<=n;++i)
	{
		while(st<=dr&&a[i]<=a[deque[dr]])
			--dr;
		deque[++dr]=i;
		if(deque[st]==(i-k))
			st++;
		if(i>=k)
			rez+=a[deque[st]];
	}
	printf("%d", rez);
}