P3426 [POI 2005] SZA-Template

You plan to print a sequence of letters on paper. To accomplish this, you decide to carve a stamp. Each use of the stamp prints **all** the letters on the stamp onto the paper. The same character at the same position may be printed multiple times. For example: using the stamp `aba` can produce `ababa` (the middle `a` is printed twice). However, since what has been printed cannot be erased, printing different characters at the same position is not allowed. For example: using the stamp `aba` cannot produce `abcba`. Because carving a stamp is not easy, you want the length of the stamp string to be as small as possible.

A non-empty string of length at most $5 \times 10^5$ (containing only lowercase letters), representing the string you want to print on the paper.

Output a single integer, the minimal possible length of the stamp string.

A stamp is `ababbaba`. The printing process is as follows: ```plain ababbababbabababbabababbababbaba ababbaba ababbaba ababbaba ababbaba ababbaba ``` Translated by ChatGPT 5