get cities from some country

get_city.cs

public Task<string> FindCity(string postalCode)
{
    var jsonStream = EmbeddedResourceHelper.FromResources("postal_codes.json");
    var dictionary = DeserializeStream<Dictionary<string, string>>(jsonStream);
    if (dictionary.ContainsKey(postalCode))
        return Task.FromResult(dictionary[postalCode]);

    var collectionRange = dictionary.Where(e => e.Key.Contains("-"));
    var result = FindCityFromRangeRecords(postalCode, collectionRange);

    return Task.FromResult(result);
}

static T DeserializeStream<T>(Stream stream)
{
    var serializer = new JsonSerializer();
    using (var reader = new StreamReader(stream))
    using (var json = new JsonTextReader(reader))
    {
        return serializer.Deserialize<T>(json);
    }
}

static string FindCityFromRangeRecords(string postalCode, IEnumerable<KeyValuePair<string, string>> collectionRange)
{
    foreach (var entry in collectionRange)
    {
        var keys = entry.Key.Split('-');
        var startRange = int.Parse(keys[0]);
        var endRange = int.Parse(keys[1]);
        var postalCodeInt = int.Parse(postalCode);
        if (postalCodeInt >= startRange && postalCodeInt <= endRange)
            return entry.Value;
    }
    return null;
}