Problem:
Score : 300 points

Problem Statement

Takahashi loves the number 7 and multiples of K.

Where is the first occurrence of a multiple of K in the sequence 7,77,777,\ldots? (Also see Output and Sample Input/Output below.)

If the sequence contains no multiples of K, print -1 instead.

Constraints

1 \leq K \leq 10^6

K is an integer.

Input

Input is given from Standard Input in the following format:

K

Output

Print an integer representing the position of the first occurrence of a multiple of K. (For example, if the first occurrence is the fourth element of the sequence, print 4.)

Sample Input 1

101

Sample Output 1

4

None of 7, 77, and 777 is a multiple of 101, but 7777 is.

Sample Input 2

2

Sample Output 2

-1

All elements in the sequence are odd numbers; there are no multiples of 2.

Sample Input 3

999983

Sample Output 3

999982

Solution in Rust (1.42.0) (judge verdict: Accepted)

#![allow(
  non_snake_case,
  unused_variables,
  unused_assignments,
  unused_mut,
  unused_imports,
  dead_code
)]
use proconio::{input, marker::*};
use std::cmp::*;
use std::collections::*;
//use std::num;
//use petgraph::unionfind::UnionFind;
//use permutohedron::LexicalPermutation as _;

//#[fastout()]
fn main() {
  input! {
      K:i64,
  }
  if K % 2 == 0 || K % 5 == 0 {
    println!("-1");
    return;
  }
  let mut k = K;
  let mut rep7 = 7;
  for i in 1..std::i64::MAX {
    if rep7 >= K {
      rep7 = rep7 % K;
    }
    if rep7 == 0 {
      println!("{}", i);
      return;
    }
    rep7 = rep7 * 10 + 7;
  }
}