Instructions: In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
Input: Guam is treated differently by what compared to FedEx, UPS, and DHL?, Context: In 1899, the local postage stamps were overprinted "Guam" as was done for the other former Spanish colonies, but this was discontinued shortly thereafter and regular U.S. postage stamps have been used ever since. Because Guam is also part of the U.S. Postal System (postal abbreviation: GU, ZIP code range: 96910–96932), mail to Guam from the U.S. mainland is considered domestic and no additional charges are required. Private shipping companies, such as FedEx, UPS, and DHL, however, have no obligation to do so, and do not regard Guam as domestic.
Output:
U.S. Postal System