def common_to_cidr(common_mask):
    """Function that returns a CIDR mask (Ex: 24)
        for a given input common mask (Ex: 255.255.255.0)"""
    commontocidr = {
        "128.0.0.0": 1,
        "192.0.0.0": 2,
        "224.0.0.0": 3,
        "240.0.0.0": 4,
        "248.0.0.0": 5,
        "252.0.0.0": 6,
        "254.0.0.0": 7,
        "255.0.0.0": 8,
        "255.128.0.0": 9,
        "255.192.0.0": 10,
        "255.224.0.0": 11,
        "255.240.0.0": 12,
        "255.248.0.0": 13,
        "255.252.0.0": 14,
        "255.254.0.0": 15,
        "255.255.0.0": 16,
        "255.255.128.0": 17,
        "255.255.192.0": 18,
        "255.255.224.0": 19,
        "255.255.240.0": 20,
        "255.255.248.0": 21,
        "255.255.252.0": 22,
        "255.255.254.0": 23,
        "255.255.255.0": 24,
        "255.255.255.128": 25,
        "255.255.255.192": 26,
        "255.255.255.224": 27,
        "255.255.255.240": 28,
        "255.255.255.248": 29,
        "255.255.255.252": 30,
        "255.255.255.254": 31,
        "255.255.255.255": 32,
    }
    return commontocidr[common_mask]