const int LG = 21;
const int FN = 400005;
const long long MOD = 1e9 + 7;
const long long INF = 1e9;
const long long INFLL = 1e18;

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<ll> vi;

#define forn(i, n) for (int (i) = 0; (i) != (n); (i)++)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define popcount(x) __builtin_popcount(x)
#define popcountll(x) __builtin_popcountll(x)
#define fi first
#define se second
#define re return
#define uniq(x) sort(all(x)); (x).resize(unique(all(x)) - (x).begin())

#ifdef LOCAL
#define dbg(x) cerr << __LINE__ << " " << #x << " " << x << endl
#define ln cerr << __LINE__ << endl
#else
#define dbg(x) void(0)
#define ln void(0)
#endif // LOCAL

int cx[4] = {-1, 0, 1, 0};
int cy[4] = {0, -1, 0, 1};

ll inq(ll x, ll y)
{
    if (!y) re 1 % MOD;
    ll l = inq(x, y / 2);
    if (y % 2) re l * l % MOD * x % MOD;
    re l * l % MOD;
}

ll rev(ll x)
{
    return inq(x, MOD - 2);
}

bool __precomputed_combinatorics = 0;
vector<ll> __fact, __ufact, __rev;

void __precompute_combinatorics()
{
    __precomputed_combinatorics = 1;
    __fact.resize(FN);
    __ufact.resize(FN);
    __rev.resize(FN);
    __rev[1] = 1;
    for (int i = 2; i < FN; i++) __rev[i] = MOD - __rev[MOD % i] * (MOD / i) % MOD;
    __fact[0] = 1, __ufact[0] = 1;
    for (int i = 1; i < FN; i++) __fact[i] = __fact[i - 1] * i % MOD, __ufact[i] = __ufact[i - 1] * __rev[i] % MOD;
}

ll fact(int x)
{
    if (!__precomputed_combinatorics) __precompute_combinatorics();
    return __fact[x];
}

ll cnk(int n, int k)
{
    if (k < 0 || k > n) return 0;
    if (!__precomputed_combinatorics) __precompute_combinatorics();
    return __fact[n] * __ufact[n - k] % MOD * __ufact[k] % MOD;
}

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n;
    cin >> n;
    vector<int> a(n + 1);
    for (int i = 1; i <= n; i++) cin >> a[i];
    sort(all(a));
    if (a[1] == 0) cout << 0, exit(0);
    if (a[n - 1] == 12) cout << 0, exit(0);
    for (int i = 0; i + 2 < a.size(); i++)
    {
        if (a[i] == a[i + 2])
        {
            cout << 0, exit(0);
        }
    }
    vector<int> tm(n + 1, -1);
    for (int i = 0; i < a.size(); i++)
    {
        if (a[i] == 0)
            tm[i] = 0;
        if (a[i] == 12)
            tm[i] = 12;
        if (i + 1 < a.size() && a[i] == a[i + 1])
            tm[i] = a[i], tm[i + 1] = 24 - a[i];
    }
    int cnt = 0;
    for (int i = 0; i < n + 1; i++) cnt += tm[i] == -1;
    int di = 0;
    for (int i = 0; i < (1 << cnt); i++)
    {
        int j = 0;
        vector<int> tm2 = tm;
        for (int k = 0; k < tm2.size(); k++)
        {
            if (tm2[k] == -1)
            {
                if ((i & (1 << j)))
                {
                    tm2[k] = 24 - a[k];
                }
                else
                {
                    tm2[k] = a[k];
                }
                j++;
            }
        }
        sort(all(tm2));
        int mn = 1e9;
        for (int j = 0; j + 1 < tm2.size(); j++)
        {
            mn = min(mn, tm2[j + 1] - tm2[j]);
        }
        mn = min(mn, 24 - tm2.back());
        di = max(di, mn);
    }
    cout << di;
}

/* Note:
Check constants at the beginning of the code.
    N is set to 4e5 but be careful in problems with large constant factor.
    Setting N in every problem is more effective.
Check corner cases.
    N = 1
No def int long long for now.
Add something here.
*/


Measured memory_bytes: 256