"""

偶奇さえ等しければいける気がしない？


"""

import sys
from sys import stdin

N,M = map(int,stdin.readline().split())

A = list(map(int,stdin.readline().split()))


Asum = sum(A)

if M % 2 == 0 and Asum % 2 == 1:
    print (-1)
    sys.exit()

assert False