N = int(input())
s = 8
buf = [1000]*s
buf_even = [1000]*s
result = 1001*1001
n = int(input())
if n % 2 == 0:
    buf_even[0] = n
buf[0] = n
for i in range(1, s):
    n = int(input())
    if n % 2 == 0:
        buf_even[i] = min(buf_even[i-1], n)
    else:
        buf_even[i] = buf_even[i-1]
    buf[i] = min(buf[i-1], n)
for i in range(s, N):
    n = int(input())
    if n % 2 == 0:
        result = min(n * buf[i % s], result)
        buf_even[i % s] = min(n, buf[(i-1) % s])
    else:
        result = min(n * buf_even[i % s], result)
    buf[i % s] = min(n, buf[(i-1) % s])
if result != 1001*1001: print(result)
else: print(-1)