#!/usr/bin/env python3
import json
import sys


subnets = [
    {
        "az": subnet.get("AvailabilityZone", ""),
        "id": subnet.get("SubnetId", ""),
        "vpc": subnet.get("VpcId", ""),
    }
    for subnet in json.load(sys.stdin).get("Subnets", [])
    if subnet.get("MapPublicIpOnLaunch")
]
subnets.sort(key=lambda subnet: (subnet["az"], subnet["vpc"], subnet["id"]))

for candidate in subnets:
    if candidate["id"] and candidate["az"] and candidate["vpc"] and any(
        sibling["id"]
        and sibling["vpc"] == candidate["vpc"]
        and sibling["az"]
        and sibling["az"] != candidate["az"]
        for sibling in subnets
    ):
        print(candidate["id"])
        break
else:
    sys.exit("no available public subnet belongs to a VPC with public subnets in two availability zones")