Digital Sum Reduction

This problem requires you to compute the digital root of an integer, i.e. repeatedly summing the digits of the number until a single-digit number is obtained. The process is as follows:

Given an integer \( n \), repeatedly compute the sum of its digits until the resulting sum is a single digit (i.e., less than 10), and output that digit.

For instance, given \( n = 9875 \), the computation proceeds as:

\( 9 + 8 + 7 + 5 = 29 \), then \( 2 + 9 = 11 \), and finally \( 1 + 1 = 2 \). Thus, the output is 2.

inputFormat

The input is provided in stdin and consists of a single integer \( n \) where \( 0 \le n \le 10^{20} \).

outputFormat

Output the single-digit digital root of the given integer. The output should be written to stdout.

## sample

9875

2

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