using System;
using System.Collections.Generic;
using System.Collections;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.IO;
using System.Reflection;
using static System.Math;
using System.Numerics;
using System.Threading;
using System.Runtime.CompilerServices;
using System.Diagnostics;
static class Program{
	const long inf=long.MaxValue>>1;
	const int mod=998244353;
	static Sc sc=new Sc();
	static void Main(){
		Pt pt=new Pt(Solve);
		pt.Sm();
	}
	static void Solve(Pt pt) {
		var (n,k)=sc.Tp2<int>();
		var a = sc.Ia2;
		St st = new St(n+1,true);
		st.Ud2(0,0,a[1]);
		for(int i = 2;i<=n;i++) {
			st.Ud2(i,i,st.Get(Max(0,i-k),i-1).d);
			st.Ud2(Max(0,i-k),i-1,a[i]);
		}
		pt.Wl(st.Get(Max(0,n-k+1),n).d);
	}
}
public class St {
	public class Mo {
		public int n;
		public long d, c = 0;
		public Mo(long d,int n) { this.d=d; this.n=n; }
		public Mo(Mo mo) { d=mo.d+mo.c; n=mo.n; }
	}
	public Mo[] dat;
	private int m = 1, cnt;
	private bool mm;
	private Mo du;
	private Func<Mo,Mo,bool> compare;
	public St(int n,bool mm) {
		this.mm=mm;
		if(mm) { du=new Mo(long.MinValue,-1); compare=CoMax; }
		else { du=new Mo(long.MaxValue,-1); compare=CoMin; }
		while(m<n) { m<<=1; }
		cnt=m+n-1;
		dat=new Mo[cnt+1];
		for(int i = m-1;i<=cnt;i++) { dat[i]=new Mo(0,i-m+1); }
		for(int i = m-2;i>=0;i--) {
			if(2*i+1>=cnt) { dat[i]=new Mo(0,-1); }
			else { dat[i]=new Mo(0,dat[2*i+1].n); }
		}
	}
	private bool CoMax(Mo x,Mo y) { return x.d>y.d; }
	private bool CoMin(Mo x,Mo y) { return x.d<y.d; }
	private Mo Fdg(int a,int b,int k,int l,int r) {
		if(dat[k].c!=0) {
			dat[k].d+=dat[k].c;
			if(2*k+2<cnt) { dat[2*k+1].c+=dat[k].c; dat[2*k+2].c+=dat[k].c; }
			else if(2*k+2==cnt) { dat[2*k+1].d+=dat[k].c; }
			dat[k].c=0;
		}
		if(r<a||b<l) { return du; }
		if(a<=l&&r<=b) { return dat[k]; }
		Mo p = Fdg(a,b,k*2+1,l,(l+r)>>1);
		Mo q = Fdg(a,b,k*2+2,(l+r+1)>>1,r);
		return compare(p,q) ? p : q;
	}
	public Mo Get(int a,int b) { return Fdg(a,b,0,0,m-1); }
	public void Ud2(int a,int b,long d) { Hn(a,b,0,0,m-1,d); }
	private Mo Hn(int a,int b,int k,int l,int r,long d) {
		if(a<=l&&r<=b) {
			dat[k].d+=dat[k].c+d;
			if(2*k+2<cnt) { dat[2*k+1].c+=dat[k].c+d; dat[2*k+2].c+=dat[k].c+d; }
			else if(2*k+2==cnt) { dat[2*k+1].d+=dat[k].c+d; }
			dat[k].c=0;
			return dat[k];
		}
		if(dat[k].c!=0) {
			dat[k].d+=dat[k].c;
			if(2*k+2<cnt) { dat[2*k+1].c+=dat[k].c; dat[2*k+2].c+=dat[k].c; }
			else if(2*k+2==cnt) { dat[2*k+1].d+=dat[k].c; }
			dat[k].c=0;
		}
		if(r>=a&&b>=l) {
			Mo p = new Mo(Hn(a,b,k*2+1,l,(l+r)>>1,d));
			Mo q = new Mo(Hn(a,b,k*2+2,(l+r+1)>>1,r,d));
			dat[k]=compare(p,q) ? p : q;
			return dat[k];
		}
		return dat[k];
	}
}
public class Pt{
	private StringBuilder sb=new StringBuilder();
	public Pt(Action<Pt> f){f(this);}
	public void W(int s){sb.Append(s);}
	public void W(long s){sb.Append(s);}
	public void W(double s){sb.Append(s);}
	public void W(decimal s){sb.Append(s);}
	public void W(char s){sb.Append(s);}
	public void W(string s){sb.Append(s);}
	public void W(object s){sb.Append(s);}
	public void W(params object[] s){sb.Append(string.Join(" ",s));}
	public void Wl(int s){sb.Append(s).AppendLine();}
	public void Wl(long s){sb.Append(s).AppendLine();}
	public void Wl(double s){sb.Append(s).AppendLine();}
	public void Wl(decimal s){sb.Append(s).AppendLine();}
	public void Wl(char s){sb.Append(s).AppendLine();}
	public void Wl(string s){sb.AppendLine(s);}
	public void Wl(object s){sb.Append(s).AppendLine();}
	public void Wl(int[] s){sb.AppendLine(string.Join(" ",s));}
	public void Wl(long[] s){sb.AppendLine(string.Join(" ",s));}
	public void Wl(double[] s){sb.AppendLine(string.Join(" ",s));}
	public void Wl(string[] s){sb.AppendLine(string.Join(" ",s));}
	public void Wl(params object[] s){sb.AppendLine(string.Join(" ",s));}
	public void Wl(){sb.AppendLine();}
	public void Sm(){Console.Write(sb);}
	public void Op(StreamWriter sw){
		sw.Write(sb);
		sw.Close();
	}
	public static bool operator ==(Pt a,Pt b){return a.sb.ToString()==b.sb.ToString();}
	public static bool operator !=(Pt a,Pt b){return a.sb.ToString()!=b.sb.ToString();}
	public override bool Equals(object obj){return false;}
	public override int GetHashCode(){return 0;}
}
public class Sc{
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	protected virtual string Rl(){return Console.ReadLine();}
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	protected virtual string[] Sp(string st){return st.Split();}
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	private T Ct<T>(string s){return (T)Convert.ChangeType(s,typeof(T));}
	public virtual int I{get{return int.Parse(Rl());}}
	public virtual long L{get{return long.Parse(Rl());}}
	public virtual double D{get{return double.Parse(Rl());}}
	public virtual string S{get{return Rl();}}
	public int[] Ia{get{return Array.ConvertAll(Sp(Rl()),int.Parse);}}
	public long[] La{get{return Array.ConvertAll(Sp(Rl()),long.Parse);}}
	public double[] Da{get{return Array.ConvertAll(Sp(Rl()),double.Parse);}}
	public string[] Sa{get{return Sp(Rl());}}
	public object[] Oa{get{return Sp(Rl());}}
	public int[] Ia2{get{return Array.ConvertAll(Sp("0 "+Rl()+" 0"),int.Parse);}}
	public int[] Ia3(string a,string b){return Array.ConvertAll(Sp(a+Rl()+b),int.Parse);}
	public int[] Ia3(int a){return Array.ConvertAll(Sp(Rl()+" "+a.ToString()),int.Parse);}
	public long[] La2{get{return Array.ConvertAll(Sp("0 "+Rl()+" 0"),long.Parse);}}
	public long[] La3(string a,string b){return Array.ConvertAll(Sp(a+Rl()+b),long.Parse);}
	public long[] La3(int a){return Array.ConvertAll(Sp(Rl()+" "+a.ToString()),long.Parse);}
	public double[] Da2{get{return Array.ConvertAll(Sp("0 "+Rl()+" 0"),double.Parse);}}
	public double[] Da3(string a,string b){return Array.ConvertAll(Sp(a+Rl()+b),double.Parse);}
	public T[] Arr<T>(int n,Func<T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f();}return a;}
	public T[] Arr<T>(int n,Func<int,T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i);}return a;}
	public T[] Arr<T>(int n,Func<string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(Sp(Rl()));}return a;}
	public T[] Arr<T>(int n,Func<int,string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i,Sp(Rl()));}return a;}
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public (T,T) Tp2<T>(){var s=Sp(Rl());return (Ct<T>(s[0]),Ct<T>(s[1]));}
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public (T,T,T) Tp3<T>(){var s=Sp(Rl());return (Ct<T>(s[0]),Ct<T>(s[1]),Ct<T>(s[2]));}
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public (T,T,T,T) Tp4<T>(){var s=Sp(Rl());return (Ct<T>(s[0]),Ct<T>(s[1]),Ct<T>(s[2]),Ct<T>(s[3]));}
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public (T,T,T,T,T) Tp5<T>(){var s=Sp(Rl());return (Ct<T>(s[0]),Ct<T>(s[1]),Ct<T>(s[2]),Ct<T>(s[3]),Ct<T>(s[4]));}
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public (T,T,T,T,T,T) Tp6<T>(){var s=Sp(Rl());return (Ct<T>(s[0]),Ct<T>(s[1]),Ct<T>(s[2]),Ct<T>(s[3]),Ct<T>(s[4]),Ct<T>(s[5]));}
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public (T1,T2) Tp2<T1,T2>(){var s=Sp(Rl());return (Ct<T1>(s[0]),Ct<T2>(s[1]));}
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public (T1,T1,T2) Tp3<T1,T2>(){var s=Sp(Rl());return (Ct<T1>(s[0]),Ct<T1>(s[1]),Ct<T2>(s[2]));}
}
public class Scr:Sc{
	private List<string> li=new List<string>();
	private int l=0;
	private bool bo=false;
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	protected override string Rl(){
		if(bo){return li[l++%li.Count];}
		li.Add(Console.ReadLine());
		return li[li.Count-1];
	}
	public void Again(){bo=true;}
}
public class Scs:Sc{
	private StreamReader sr;
	public Scs(string t){sr=new StreamReader(t);}
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	protected override string Rl(){return sr.ReadLine();}
	public void Close(){sr.Close();}
}
public class Sc2:Sc{
	private string[] sps=new string[]{" ","　","\t"};
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	protected override string[] Sp(string st){return st.Split(sps,StringSplitOptions.RemoveEmptyEntries);}
	public override int I{get{return int.Parse(Sp(Rl())[0]);}}
	public override long L{get{return long.Parse(Sp(Rl())[0]);}}
	public override double D{get{return double.Parse(Sp(Rl())[0]);}}
	public override string S{get{return Sp(Rl())[0];}}
}
public class Scs2:Sc2{
	private StreamReader sr;
	public Scs2(string t){sr=new StreamReader(t);}
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	protected override string Rl(){return sr.ReadLine();}
	public void Close(){sr.Close();}
}
public class Sct:Sc{
	private List<string> li=new List<string>();
	private int l=0;
	public void Add(int s){li.Add(s.ToString());}
	public void Add(long s){li.Add(s.ToString());}
	public void Add(double s){li.Add(s.ToString());}
	public void Add(string s){li.Add(s.ToString());}
	public void Add(object s){li.Add(s.ToString());}
	public void Add(int[] s){li.Add(string.Join(" ",s));}
	public void Add(long[] s){li.Add(string.Join(" ",s));}
	public void Add(double[] s){li.Add(string.Join(" ",s));}
	public void Add(string[] s){li.Add(string.Join(" ",s));}
	public void Add(params object[] s){li.Add(string.Join(" ",s));}
	protected override string Rl(){return li[l++];}
	public void Clear(){li.Clear();l=0;}
	public void Again(){l=0;}
	public void Pf(){Console.WriteLine(string.Join("\n",li));}
}