package com.company;

import java.io.BufferedInputStream;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;

public class Main {
    static int[][]ab;
    static int ans, cnt;
    public static void main(String[] args) {
        Scanner sc = new Scanner(new BufferedInputStream(System.in));
        while (true) {
            int N = sc.nextInt();
            if (N == 0)
                break;
            int[] arr = new int[N];
            for (int i = 0; i < arr.length; i++) {
                arr[i] = sc.nextInt();
            }
            int SN = (N - 1) * N / 2;
            ab = new int[SN][3];
            //a + b = b - c
            cnt = 0;
            for (int i = 0; i < N; i++) {
                for (int j = i + 1; j < N; j++) {
                    ab[cnt][0] = arr[i] + arr[j];
                    ab[cnt][1] = i;
                    ab[cnt++][2] = j;
                }
            }
            Arrays.sort(ab, new Comparator<int[]>() {
                @Override
                public int compare(int[] o1, int[] o2) {
                    return o1[0] - o2[0];
                }
            });

            ans = Integer.MIN_VALUE;
            for (int i = 0; i < N; i++) {
                for (int j = i + 1; j < N; j++) {
                    int c_d = arr[i] - arr[j];
                    f(i, j, c_d, arr[i]);
                    f(i, j, -c_d, arr[j]);
                }
            }
            if (ans ==  Integer.MIN_VALUE)
                System.out.println("no solution");
            else
                System.out.println(ans);
        }
    }
    public static void f(int i, int j, int c_d, int d) {
        int l = 0, r = cnt;
        while (l < r - 1) {
            int mid = (l + r) / 2;
            if (ab[mid][0] < c_d )
                l = mid;
            else
                r = mid;
        }
        for (int k = l + 1; k < cnt && ab[k][0] == c_d; k++) {
            if (ab[k][2] == i || ab[k][2] == j || ab[k][1] == i || ab[k][1] == j) continue;
            ans = Math.max(ans, d);
        }
    }
}