#include <stdio.h>

#define Nmax 5000100

int n,k,st,dr,a[Nmax],deque[Nmax];
long long sum;

int main()
{
	int i;
	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;

			if(st<=dr && deque[st] == i-k) ++st;

			deque[++dr]=i;

			if(i>=k) sum+=a[deque[st]];
		}
	printf("%lld",sum);
	return 0;
}