import re


def find_ipv4_with_subnet(string):
    """
    Find and return IPv4 address with subnet inside a string.
    This function will only return an ipv4 address with a subnet



    :param string: (str) The string to search for ipv6 with subnet(i.e. "Successfully added Subnet 10.34.33.20/30")
    :return: (str) the found ipv6 address with subnet (i.e. '10.34.33.20/30')
    """
    ip = re.search(r"([0-9]{1,3}\.){3}[0-9]{1,3}/([0-9])([0-9])?", string)

    if ip:
        return ip.group()

    return None