#define NOSTDCPP
//#define Cpp11
//#define Linux_System
#ifndef NOSTDCPP
	
#include <bits/stdc++.h>
	
#else
	
#include <algorithm>
#include <bitset>
#include <cassert>
#include <climits>
#include <complex>
#include <cstring>
#include <cstdio>
#include <deque>
#include <exception>
#include <functional>
#include <iomanip>
#include <iostream>
#include <istream>
#include <iterator>
#include <list>
#include <map>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
	
#endif
	
# ifdef Linux_System
# define getchar getchar_unlocked
# define putchar putchar_unlocked
# endif
	
# define RESET(_) memset(_, 0, sizeof(_))
# define RESET_(_, val) memset(_, val, sizeof(_))
# define fi first
# define se second
# define pb push_back
# define midf(x, y) ((x + y) >> 1)
# define DXA(_) ((_ << 1))
# define DXB(_) ((_ << 1) | 1)
	
# define next __Chtholly__
# define x1 __Mercury__
# define y1 __bbtl04__
# define index __ikooo__
	
using namespace std;
	
typedef long long ll;
typedef unsigned long long ull;
typedef vector <int> vi;
typedef set <int> si;
typedef pair <int, int> pii;
typedef long double ld;
	
const int MOD = 1e9 + 7;
const int maxn = 1009;
const int maxm = 300009;
const int inf = 1e9;
const double pi = acos(-1.0);
const double eps = 1e-6;
	
ll myrand(ll mod){return ((ll)rand() << 32 ^ (ll)rand() << 16 ^ rand()) % mod;}
	
template <class T>
inline bool scan_d(T & ret)
{
	char c;
	int sgn;
	if(c = getchar(), c == EOF)return false;
	while(c != '-' && (c < '0' || c > '9'))c = getchar();
	sgn = (c == '-') ? -1 : 1;
	ret = (c == '-') ? 0 : (c - '0');
	while(c = getchar(), c >= '0' && c <= '9')
		ret = ret * 10 + (c - '0');
	ret *= sgn;
	return true;
}
#ifdef Cpp11
template <class T, class ... Args>
inline bool scan_d(T & ret, Args & ... args)
{
	scan_d(ret);
	scan_d(args...);
}
#define cin.tie(0); cin.tie(nullptr);
#define cout.tie(0); cout.tie(nullptr);
#endif
inline bool scan_ch(char &ch)
{
	if(ch = getchar(), ch == EOF)return false;
	while(ch == ' ' || ch == '\n')ch = getchar();
	return true;
}
	
template <class T>
inline void out_number(T x)
{
	if(x < 0)
	{
		putchar('-');
		out_number(- x);
		return ;
	}
	if(x > 9)out_number(x / 10);
	putchar(x % 10 + '0');
}
	
int n, ans, l, r;
int A[maxn];
	
int main()
{
	while(scanf("%d", &n) && n)
	{
		ans = -inf;
		for(int i = 1; i <= n; ++ i) scanf("%d", A + i);
		if(n <= 3) {puts("no solution"); continue;}
		sort(A + 1, A + 1 + n);
		for(int i = n; i >= 1; -- i)
		{
			for(int j = n; j >= 1; -- j)
			{
				if(i == j) continue;
				l = 1, r = j - 1;
				while(l < r)
				{
					if(A[l] + A[r] == A[i] - A[j]) {ans = A[i]; break;}
					if(A[l] + A[r] < A[i] - A[j]) ++ l;
					else -- r;
				}
				if(ans != -inf) break;
			}
			if(ans != -inf) break;
		}
		/*
		if(A[1] < 0)
		{
			for(int i = 1; i <= n; ++ i)
				for(int j = i + 1; j <= n; ++ j)
				{
					if(i == j) continue;
					l = j + 1, r = n;
					while(l < r)
					{
						if(A[l] + A[r] == A[i] - A[j]) {ans = A[i]; break;}
						if(A[l] + A[r] < A[i] - A[j]) ++ l;
						else -- r;
					}
					if(ans != -inf) break;
				}
		}
		*/
		ans == -inf ? puts("no solution") : printf("%d\n", ans);
	}
	return 0;
}
/*
5
2 3 5 7 12
5
2 16 64 256 1024
6
-6 -5 -4 -3 -2 -1
0
*/