//BISMILLAHIR RAHMANIR RAHIM
#include<stdio.h>
#include<string.h>
#include<math.h>
#include<stdlib.h>
#include<queue>
#include<set>
#include <iostream>
#include<stack>
#include<map>
#include<string>
#include<vector>
#include<algorithm>
#define N 1000000
#define sn scanf
#define pf printf
#define pb push_back
#define mp make_pair

const double PI=2.0*acos(0);

typedef long long int ll;
using namespace std;
struct T{
ll a,b;
bool operator < (const T &bb)const
{
    return a>bb.a;
}
};
ll inf=1000000000000000LL,dp[1001001],ar[100000];
int main()
{
   ll i,j,k,l,t,cs=1,r=1,s,m,n,a,b,c,d,e,f,g,h,u,v;

    //freopen(".txt","r",stdin);
    sn("%lld %lld",&n,&k);
    for(i=1;i<=n;i++)
    {
        sn("%lld",&ar[i]);
    }
    for(i=0;i<=n;i++)
    {
        dp[i]=inf;
    }
    dp[0]=0;
    for(i=1;i<=n;i++)
    {
        u=min(n,i+k);
        dp[u]=min(dp[u],dp[max(0ll,i-k-1)]+ar[i]);
    }
    pf("%lld\n",dp[n]);
    return 0;

}

/*
#include <bits/stdc++.h>
  #define _ ios_base::sync_with_stdio(0);cin.tie(0);
*/