#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdio>
#include <cmath>
#define ll long long
#define max 100010
using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
ll n,k,x[max],now,sum,y[max];
inline ll read()
{
	char tmp=getchar();
	ll f=1,ans=0;
	while(tmp<'0'||tmp>'9')
	{
		if(tmp=='-')
			f=-f;
		tmp=getchar();
	}
	while(tmp>='0'&&tmp<='9')
	{
		ans=ans*10-'0'+tmp;
		tmp=getchar();
	}
	return ans*f;	
}
int main(int argc, char** argv)
{
	freopen("qwa.in","r",stdin);
	freopen("qwa.out","w",stdout);
	n=read();
	k=read();
// 	printf("%lld %lld\n",n,k);
	for(ll i=1;i<=n;i++)
	{
		x[i]=read();
		//printf("%lld\n",x[i]);
		y[i]+=x[i]+y[i-1];
	}
	ll pot=0xfffffff;
	for(ll i=1;i<=n+1-k;i++)
	{
		ll ans=0,tmp=k,tot=0;
		tot=y[i+k-1]-y[i-1];
		for(ll j=i;j<i+k;j++)
		{
			ans+=tot-tmp*x[j];
			tot-=x[j];
			tmp--;
		}
		pot=min(ans,pot);
	}                    
	printf("%lld",pot);                                                                                                                                                                                                   
	return 0;
}