给定一个长度恰好为 9 的字符串 S，该字符串由数字0～9组成。在 S 中每个数字恰好只出现1次，显然，0～9一共有10个数字，现在缺失了其中的一个，请打印出在 S 中缺少的唯一数字。
Time Limit: 2 sec / Memory Limit: 1024 MB
Score : 100100 points
Problem Statement
You are given a string SS of length exactly 99 consisting of digits. One but all digits from 0 to 9 appear exactly once in SS.
Print the only digit missing in SS.
Constraints
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SS is a string of length 99 consisting of digits.
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All characters in SS are distinct.
Input
Input is given from Standard Input in the following format:
SS
Output
Print the only digit missing in SS.