Duplicate SSN

The U.S. Social Security Administration has made a serious mistake. While assigning new Social Security numbers (SSNs) to U.S. citizens, it accidentally issued some duplicate numbers. Fortunately, the mistake was caught early, and a list of all possible duplicates is available. The Social Security Administration must contact everyone who does not have a unique SSN. Your task is to read the list of Social Security numbers, find all the duplicates, and print those duplicates in ascending order.

The input is a list of Social Security numbers, one per line. The input is terminated by the Social Security number 000-00-0000, which is not counted as a duplicate.

Print every Social Security number that appears more than once in the input, in ascending order. Print one number per line, and print each duplicated number only once even if it appears several times.