#include<cstdio>
#define nmax 500010
int n,k,a[nmax],deque[nmax],f,b;
long long s=0;
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]);
	
f=1;b=0;
for(i=1;i<=n;i++)
{
	while(f<=b&&a[i]<=a[deque[b]]) 
		b--;
	deque[b++]=i;
	if(deque[f]==i-k) f++;
	
	if(i>=k) s+=a[deque[f]];
}

printf("%lld",s);
return 0;
}