{"raw_statement":[{"iden":"problem statement","content":"A subsequence of a string $S$ is a string that can be obtained by deleting zero or more characters from $S$ without changing the order of the remaining characters. For example, `arc`, `artistic` and (an empty string) are all subsequences of `artistic`; `abc` and `ci` are not.\nYou are given a string $A$ consisting of lowercase English letters. Find the shortest string among the strings consisting of lowercase English letters that are not subsequences of $A$. If there are more than one such string, find the lexicographically smallest one among them."},{"iden":"constraints","content":"*   $1 \\leq |A| \\leq 2 \\times 10^5$\n*   $A$ consists of lowercase English letters."},{"iden":"input","content":"Input is given from Standard Input in the following format:\n\n$A$"},{"iden":"sample input 1","content":"atcoderregularcontest"},{"iden":"sample output 1","content":"b\n\nThe string `atcoderregularcontest` contains `a` as a subsequence, but not `b`."},{"iden":"sample input 2","content":"abcdefghijklmnopqrstuvwxyz"},{"iden":"sample output 2","content":"aa"},{"iden":"sample input 3","content":"frqnvhydscshfcgdemurlfrutcpzhopfotpifgepnqjxupnskapziurswqazdwnwbgdhyktfyhqqxpoidfhjdakoxraiedxskywuepzfniuyskxiyjpjlxuqnfgmnjcvtlpnclfkpervxmdbvrbrdn"},{"iden":"sample output 3","content":"aca"}],"translated_statement":null,"sample_group":[],"show_order":["default"],"formal_statement":null,"simple_statement":null,"has_page_source":true}