#include<cstdio>

#include<cstring>

#include<algorithm>

#define LL long long

#define inf 99999999999999LL

using namespace std;

const int M=;

int read(){

    int ans=,f=,c=getchar();

    while(c<''||c>''){if(c=='-') f=-; c=getchar();}

    while(c>=''&&c<=''){ans=ans*+(c-''); c=getchar();}

    return ans*f;

}

LL ans,mn=inf,f[M];

int w[M],head,tail,k,n;

struct node{int pos; LL v;}q[M];f

int main()

{

    n=read(); k=read();

    for(int i=;i<=n;i++) w[i]=read(),ans+=w[i];

    for(int i=;i<=n;i++){

        f[i]=q[head].v+w[i];

        while(head<=tail&&q[tail].v>f[i]) tail--;

        q[++tail].v=f[i]; q[tail].pos=i;

        while(head<=tail&&q[head].pos<i-k) head++;

    }

    for(int i=n-k;i<=n;i++) mn=min(mn,f[i]);

    printf("%lld\n",ans-mn);

    return ;

}