27

s = 6
N = int(input())
result = 1000*1000
a = [1000]*s
n = int(input())
if n % 2 != 0:
    a[0] = n
for i in range(1, s):
    n = int(input())
    if n % 2 != 0:
        a[i] = min(n, a[i-1])
for i in range(s, N):
    n = int(input())
    if n % 2 != 0:
        result = min(n*a[i % s], result)
        a[i % s] = min(a[(i-1) % s], n)
if result % 2 != 0:
    print(result)
else:
    print(-1)