from collections import Counter
import sys

N = int(input())
ds = list(map(int,input().split()))
ctr = Counter(ds)
if 0 in ctr:
    print(0)
    sys.exit()

hs = (1 << 24) + 1
undef = []
for d,c in ctr.items():
    if c > 2:
        print(0)
        sys.exit()
    elif c == 2:
        hs |= (1 << d)
        hs |= (1 << (24-d))
    else: #c == 1
        undef.append(d)

ans = 0
for i in range(2**len(undef)):
    _hs = hs
    for j,u in enumerate(undef):
        if (i >> j) & 1:
            _hs |= (1 << u)
        else:
            _hs |= (1 << (24-u))
    min_interval = 24
    prev = 0
    for k in range(1,25):
        if (_hs >> k) & 1 == 0: continue
        min_interval = min(min_interval, k - prev)
        prev = k
    ans = max(ans, min_interval)
print(ans)
