#include <bits/stdc++.h>

#include <iostream>

#include <cstdio>

#include <cstring>

#include <algorithm>

#include <cmath>

using namespace std;

#define For(i,j,n) for(int i=j;i<=n;i++)

#define mst(ss,b) memset(ss,b,sizeof(ss));

typedef  long long LL;

template<class T> void read(T&num) {

    char CH; bool F=false;

    for(CH=getchar();CH<''||CH>'';F= CH=='-',CH=getchar());

    for(num=;CH>=''&&CH<='';num=num*+CH-'',CH=getchar());

    F && (num=-num);

}

int stk[], tp;

template<class T> inline void print(T p) {

    if(!p) { puts(""); return; }

    while(p) stk[++ tp] = p%, p/=;

    while(tp) putchar(stk[tp--] + '');

    putchar('\n');

}

const LL mod=1e9+;

const double PI=acos(-1.0);

const int inf=1e9;

const int N=3e6+;

const int maxn=1e3+;

const double eps=1e-;

int a[maxn],n,ans;

struct node

{

    int a,b;

};

vector<node>ve[*maxn];

map<int,int>mp;

int check(int x,int y)

{

        int temp=mp[x-y];

        int len=ve[temp].size();

        For(k,,len-)

        {

             int fa=ve[temp][k].a,fb=ve[temp][k].b;

             if(fa!=x&&fa!=y&&fb!=x&&fb!=y)

             {

                 ans=max(ans,x);

                 return x;

             }

        }

        return -inf;

}

int main()

{

        while()

        {

            mp.clear();

            For(i,,*maxn-)ve[i].clear();

            read(n);

            if(!n)break;

            int cnt=;

            For(i,,n)read(a[i]);

            For(i,,n)

                For(j,i+,n)

                  {

                    if(!mp[a[i]+a[j]])

                    {

                        cnt++;

                        mp[a[i]+a[j]]=cnt;

                        node d;

                        d.a=a[i],d.b=a[j];

                        ve[cnt].push_back(d);

                    }

                    else

                    {

                        int temp=mp[a[i]+a[j]];

                        node d;

                        d.a=a[i],d.b=a[j];

                        ve[temp].push_back(d);

                    }

                  }

            ans=-inf;

            For(i,,n)

            {

                For(j,i+,n)

                {

                    if(mp[a[i]-a[j]])ans=max(ans,check(a[i],a[j]));

                    if(mp[a[j]-a[i]])ans=max(ans,check(a[j],a[i]));

                }

            }

            if(ans==-inf)cout<<"no solution"<<endl;

            else cout<<ans<<endl;

        }

        return ;

}