3539：Daizhenyang's Letter

One day, Daizhenyang is wandering in BUPT campus, thinking about having a girlfriend. Out of nowhere, a breath-taking beautiful girl came by, Daizhenyang was shocked by her beauty and was too stunned to say hi.
There's an old saying, "Once there was true love for me but I did not cherish it. When it slipped away between my fingers, I began to regret. That is the saddest thing in life. If God could give me a second chance, I would tell the girl 'I love you!'. If there should be a time limit on this love, I wish it would be 10000 years." Regretting is what Daizhengyang is being through. He wants to make everything right, so he figured out her mail address and decides to send a love letter.
After thinking again and again for a long time, Daizhenyang picked up some keywords to express his love and emotion. However, Daizhenyang is busy on his eternal lasting enterprise, unifying all kinds of ACM/ICPC problems to network flow, he wants to make this letter as short as possible. You can help him on this holy project, making his dream come true.

There are multiple cases in the input file.
For each test case:
Line 1: an single integer N ( 0<N<=12 ) , represents the number of keywords.
Line 2 - N+1: a keyword in each line, keywords only consist of uppercase letters ( for sincerity ) , length is less than 56.

For each test case, output one line, begin with "Case #k: ", k is the case number, followed by the letter required. If there're several solutions output the lexicographically smaller one.