Statement

Count and return the number of good subsequences in the given string s. You may return the modulo $10^9 + 7$ of the count.

A subsequence is a sequence formed from another sequence by deleting some or no elements while keeping the order of the remaining elements unchanged.
A good subsequence is a subsequence of a string if it is not empty and the frequency of each character is the same.

Constraints:

Examples

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