import java.io.File;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class test {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int m=sc.nextInt();
        int n=sc.nextInt();
        int [] o=new int[n];
        for(int i=0;i<n;i++){
            o[i]=sc.nextInt();
        }
        int [] s=new int[m];
        int [] sum=new int[m];
        for(int i=0;i<m;i++){

            if(i<m-1){
                s[i]=1;
                sum[i]=o[i];
            }
        }
        sum[m-1]=0;
        s[m-1]=n-m+1;
        for(int i=m-1;i<n;i++){
            sum[m-1]+=o[i];

        }
        spilt(sum,s,o);
    }
    public static void spilt(int [] sum,int [] s,int[] o){
        List<Integer> list=new ArrayList<>();
        int max=0;
        int i=0;
        while (i<10) {
            list = max(sum);
            max=list.get(1);
            int index = list.get(0);
            if (index == 0) {
                sum[index] = sum[index] - o[s[index] - 1];
                sum[index + 1] = sum[index + 1] + o[s[index] - 1];
                s[index] -= 1;
                s[index + 1] += 1;
            } else if (index == sum.length - 1) {
                sum[index] = sum[index] - o[o.length - s[index]];
                sum[index - 1] = sum[index - 1] + o[o.length - s[index]];
                s[index] -= 1;
                s[index - 1] += 1;
            } else {
                if (sum[index - 1] < sum[index + 1]) {
                    sum[index] = sum[index] - o[sum1(s, index)];
                    sum[index - 1] = sum[index - 1] + o[sum1(s, index)];
                    s[index] -= 1;
                    s[index - 1] += 1;
                } else {
                    sum[index] = sum[index] - o[sum1(s, index + 1) - 1];
                    sum[index + 1] = sum[index + 1] + o[sum1(s, index + 1) - 1];
                    s[index] -= 1;
                    s[index + 1] += 1;
                }
            }
            i++;
        }
        System.out.println(max);
    }
    public static int sum1(int[] s,int index){
        int sum=0;
        for(int i=0;i<index;i++){
            sum+=s[i];
        }
        return sum;
    }
    public static List<Integer> max(int[] sum){
        List<Integer> list=new ArrayList<>();
        int max=sum[0];
        int index=0;
        for(int i=1;i<sum.length;i++){
            if(sum[i]>max){
                max=sum[i];
                index=i;
            }
        }
        list.add(index);
        list.add(max);
        return list;
    }
}