import sys

# sys.setrecursionlimit(1000005)
# sys.set_int_max_str_digits(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = -1-(-1 << 31)
inf = -1-(-1 << 63)
md = 10**9+7
# md = 998244353

def ok():
    if 0 in dd: return False
    if len(dd) == 2: return dd[0] == dd[1]
    if len(set(dd)) != 2: return False
    s = set()
    t = set()
    for i, d in enumerate(dd):
        if i%4 == 0 or i%4 == 1:
            s.add(d)
        else:
            t.add(d)
    return len(s) == len(t) == 1

n = II()
aa = LI()
dd = [(aa[i+1]-aa[i])%3 for i in range(2*n)]
if ok():
    print(dd[-1])
else:
    print(0)