#include<stdio.h>
long n,k,v[5000010],deque[5000010];
long long suma;
int main()
{
long i,u=0,p=1;
freopen("deque.in","r",stdin);
freopen("deque.out","w",stdout);
scanf("%ld%ld",&n,&k);
for (i=1;i<=n;++i)
	scanf("%ld",&v[i]);
for (i=1;i<=n;++i)
{
while(p<=u && v[i]<v[deque[u]])
	u--;
deque[++u]=i;
if(deque[p]<=i-k)
	p++;
if (i>=k)
		suma+=v[deque[p]];
}
printf("%lld",suma);
return 0;
}