{"raw_statement":[{"iden":"problem statement","content":"You are given a string $S$ of length $N$. Among its subsequences, count the ones such that all characters are different, modulo $10^9+7$. Two subsequences are considered different if their characters come from different positions in the string, even if they are the same as strings.\nHere, a subsequence of a string is a concatenation of **one or more** characters from the string without changing the order."},{"iden":"constraints","content":"*   $1 \\leq N \\leq 100000$\n*   $S$ consists of lowercase English letters.\n*   $|S|=N$"},{"iden":"input","content":"Input is given from Standard Input in the following format:\n\n$N$\n$S$"},{"iden":"sample input 1","content":"4\nabcd"},{"iden":"sample output 1","content":"15\n\nSince all characters in $S$ itself are different, all its subsequences satisfy the condition."},{"iden":"sample input 2","content":"3\nbaa"},{"iden":"sample output 2","content":"5\n\nThe answer is five: `b`, two occurrences of `a`, two occurrences of `ba`. Note that we do not count `baa`, since it contains two `a`s."},{"iden":"sample input 3","content":"5\nabcab"},{"iden":"sample output 3","content":"17"}],"translated_statement":null,"sample_group":[],"show_order":["default"],"formal_statement":null,"simple_statement":null,"has_page_source":true}