#include<bits/stdc++.h>

using namespace std;

const int N=1e4+10;

int n,m;

int w[N]={0};

priority_queue<int,vector<int>,greater<int >> q;

int cmp(int a,int b)

{

    return a>b;

}

int main()

{

    cin>>n>>m;

    for(int i=1;i<=n;i++) scanf("%d",&w[i]);

//    sort(w+1,w+1+n,cmp);

//    for(int i=1;i<=n;i++) printf("%d",w[i]);

    if(n<=m)

    {

        cout<<w[1];

        return 0;

    }

    for(int i=1;i<=m;i++)

    {

        q.push(w[i]);

//        cout<<w[i]<<" ";

    }

    for(int i=m+1;i<=n;i++)//dfasdf

    {

        int t=q.top();

//        cout<<q.top()<<" ";

//        if(i<=m) t+=w[i+m];

//        else

        t+=w[i];

        q.pop();

        q.push(t);

//        cout<<"t:"<<t<<"           ";

    }

    while(q.size()-1) q.pop();

//    cout<<q.top()<<" ",

    cout<<q.top();

    return 0;

}