### BUGGY CODE ###

import math
#import sys
#input = sys.stdin.readline

def make_divisors(n):
    divisors = []
    for i in range(1, int(n**0.5)+1):
        if n % i == 0:
            divisors.append(i)
            if i != n // i:
                divisors.append(n//i)

    # divisors.sort()
    return divisors

def ValueToBits(x,digit):
    res = [0 for i in range(digit)]
    now = x
    for i in range(digit):
        res[i]=now%2
        now = now >> 1
    return res

def BitsToValue(arr):
    n = len(arr)
    ans = 0
    for i in range(n):
        ans+= arr[i] * 2**i
    return ans

def ZipArray(a):
    aa = [[a[i],i]for i in range(n)]

    aa.sort(key = lambda x : x[0])
    for i in range(n):
        aa[i][0]=i+1
    aa.sort(key = lambda x : x[1])
    b=[aa[i][0] for i in range(len(a))]
    return b

def ValueToArray10(x, digit):
    ans = [0 for i in range(digit)]
    now = x
    for i in range(digit):
        ans[digit-i-1] = now%10
        now = now //10
    return ans

def Zeros(a,b):
    if(b<=-1):
        return [0 for i in range(a)]
    else:
        return [[0 for i in range(b)] for i in range(a)]

def AddV2(v,w):
    return [v[0]+w[0],v[1]+w[1]]

dir4 = [[1,0],[0,1],[-1,0],[0,-1]]


def clamp(x,y,z):
    return max(y,min(z,x))

class Bit:
    def __init__(self, n):
        self.size = n
        self.tree = [0] * (n + 1)
 
    def sum(self, i):
        s = 0
        while i > 0:
            s += self.tree[i]
            i -= i & -i
        return s
 
    def add(self, i, x):
        while i <= self.size:
            self.tree[i] += x
            i += i & -i
            
#
def Zaatsu(a):
    a.sort()
    now = a[0][0]
    od = 0
    for i in range(n):
        if(now==a[i][0]):
            a[i][0]=od
        else:
            now = a[i][0]
            od+=1
            a[i][0] = od
    
    a.sort(key = lambda x : x[1])
    return a

class UnionFind:
    def __init__(self, n):
        self.par = [i for i in range(n+1)]
        self.rank = [0] * (n+1)

    # 検索
    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]

    # 併合
    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if self.rank[x] < self.rank[y]:
            self.par[x] = y
        else:
            self.par[y] = x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1

    # 同じ集合に属するか判定
    def same_check(self, x, y):
        return self.find(x) == self.find(y)


'''
def cmb(n, r, p):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % p

p = 2
N = 10 ** 6 + 2
fact = [1, 1]  # fact[n] = (n! mod p)
factinv = [1, 1]  # factinv[n] = ((n!)^(-1) mod p)
inv = [0, 1]  # factinv 計算用

for i in range(2, N + 1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    factinv.append((factinv[-1] * inv[-1]) % p)

'''

def rl(x):
    return range(len(x))

# a = list(map(int, input().split()))

#################################################
#################################################
#################################################
#################################################


#11-

n = int(input())

aa = list(map(int, input().split()))
t = [0 for i in range(13)]
a=[]

for i in aa:
    
    if(t[i]<=1):
        t[i]+=1
        a.append(i)
    elif(t[i]==2 or i==0):
        print(0)
        exit()
    
#print(a)
n = len(a)

b = [0 for i in range(25)]
ans = 0
count = 0

for i in range(2**(n-1)):
    count +=1
    for j in range(25):
        b[j]=0
    b[0]=1
    b[24]=1
    for j in range(n):
        if((i>>j) & 1):
            b[24-a[j]] += 1
        else:
            b[a[j]] += 1
    minim = 24
    prev = -24
    for j in range(0,25):
        if(b[j]==1):
            minim = min(minim, j-prev)
            prev = j
        elif(b[j]>=2):
            minim = 0
            break
    ans = max(ans,minim)
    #print(b)

print(ans)
#print(count)



































































### FIXED CODE ###

import math
#import sys
#input = sys.stdin.readline

def make_divisors(n):
    divisors = []
    for i in range(1, int(n**0.5)+1):
        if n % i == 0:
            divisors.append(i)
            if i != n // i:
                divisors.append(n//i)

    # divisors.sort()
    return divisors

def ValueToBits(x,digit):
    res = [0 for i in range(digit)]
    now = x
    for i in range(digit):
        res[i]=now%2
        now = now >> 1
    return res

def BitsToValue(arr):
    n = len(arr)
    ans = 0
    for i in range(n):
        ans+= arr[i] * 2**i
    return ans

def ZipArray(a):
    aa = [[a[i],i]for i in range(n)]

    aa.sort(key = lambda x : x[0])
    for i in range(n):
        aa[i][0]=i+1
    aa.sort(key = lambda x : x[1])
    b=[aa[i][0] for i in range(len(a))]
    return b

def ValueToArray10(x, digit):
    ans = [0 for i in range(digit)]
    now = x
    for i in range(digit):
        ans[digit-i-1] = now%10
        now = now //10
    return ans

def Zeros(a,b):
    if(b<=-1):
        return [0 for i in range(a)]
    else:
        return [[0 for i in range(b)] for i in range(a)]

def AddV2(v,w):
    return [v[0]+w[0],v[1]+w[1]]

dir4 = [[1,0],[0,1],[-1,0],[0,-1]]


def clamp(x,y,z):
    return max(y,min(z,x))

class Bit:
    def __init__(self, n):
        self.size = n
        self.tree = [0] * (n + 1)
 
    def sum(self, i):
        s = 0
        while i > 0:
            s += self.tree[i]
            i -= i & -i
        return s
 
    def add(self, i, x):
        while i <= self.size:
            self.tree[i] += x
            i += i & -i
            
#
def Zaatsu(a):
    a.sort()
    now = a[0][0]
    od = 0
    for i in range(n):
        if(now==a[i][0]):
            a[i][0]=od
        else:
            now = a[i][0]
            od+=1
            a[i][0] = od
    
    a.sort(key = lambda x : x[1])
    return a

class UnionFind:
    def __init__(self, n):
        self.par = [i for i in range(n+1)]
        self.rank = [0] * (n+1)

    # 検索
    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]

    # 併合
    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if self.rank[x] < self.rank[y]:
            self.par[x] = y
        else:
            self.par[y] = x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1

    # 同じ集合に属するか判定
    def same_check(self, x, y):
        return self.find(x) == self.find(y)


'''
def cmb(n, r, p):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % p

p = 2
N = 10 ** 6 + 2
fact = [1, 1]  # fact[n] = (n! mod p)
factinv = [1, 1]  # factinv[n] = ((n!)^(-1) mod p)
inv = [0, 1]  # factinv 計算用

for i in range(2, N + 1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    factinv.append((factinv[-1] * inv[-1]) % p)

'''

def rl(x):
    return range(len(x))

# a = list(map(int, input().split()))

#################################################
#################################################
#################################################
#################################################


#11-

n = int(input())

aa = list(map(int, input().split()))
t = [0 for i in range(13)]
a=[]

for i in aa:
    if(i==0):
        print(0)
        exit()
    if(t[i]<=1):
        t[i]+=1
        a.append(i)
    elif(t[i]==2):
        print(0)
        exit()
#print(a)
n = len(a)
if(t[1]>=1):
    print(1)
    exit()

b = [0 for i in range(25)]
ans = 0
count = 0

for i in range(2**(n-1)):
    count +=1
    for j in range(25):
        b[j]=0
    b[0]=1
    b[24]=1
    for j in range(n):
        if((i>>j) & 1):
            b[24-a[j]] += 1
        else:
            b[a[j]] += 1
    minim = 24
    prev = -24
    for j in range(0,25):
        if(b[j]==1):
            minim = min(minim, j-prev)
            prev = j
        elif(b[j]>=2):
            minim = 0
            break
    ans = max(ans,minim)
    #print(b)

print(ans)
#print(count)