Calculate the Digit Root

Given a non-negative integer \(n\), compute its digit root by repeatedly summing its digits until a single-digit number is obtained. More formally, if \(n\) is expressed in its decimal representation as \(n = d_k d_{k-1} \ldots d_1\), then the digit root is obtained by computing:

\(n_1 = d_k + d_{k-1} + \cdots + d_1\), and if \(n_1 \ge 10\) then continue the process until a single-digit number is reached.

For example, for \(n = 456\):

\(4+5+6=15\) and then \(1+5=6\), so the digit root is 6.

inputFormat

The input consists of a single non-negative integer \(n\) on one line. You may assume that \(0 \le n \le 10^{18}\).

outputFormat

Output one line containing the digit root of \(n\).

## sample

456

6

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