31520번 - Champernowne Verification 다국어

문제

The $k^{\text{th}}$ Champernowne word is obtained by writing down the first $k$ positive integers and concatenating them together. For example, the 10ドル^{\text{th}}$ Champernowne word is 12345678910ドル$.

Given a positive integer $n,ドル determine if it is a Champernowne word, and if so, which word.

입력

The first line contains a single integer, $n$ (1ドル \le n \le 10^9$). $n$ will not have leading zeroes.

출력

If $n$ is the $k^{\text{th}}$ Champernowne word, output $k$. Otherwise, output $-1$.

제한

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