First Non-Repeating Character

Given a string s, your task is to find the first character that does not repeat in the string. If every character repeats, output an underscore (_).

For example, for the string swiss, the first non-repeating character is w, while for aabbcc no character appears exactly once, so the output should be _.

The solution should be implemented such that it reads input from stdin and writes the result to stdout.

Note: Use the following LaTeX formatted explanation for counting the occurrences of characters:

$$\text{count}(c)=\text{number of times character } c \text{ appears in } s.$$

inputFormat

The input consists of a single line containing the string s (which can include letters, digits, symbols, etc.).

The string is read from stdin.

outputFormat

Output a single character which is the first non-repeating character in the string. If there is no such character, output an underscore (_).

The result is printed to stdout.

## sample

swiss

w