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 Python (3.8.2) (judge verdict: Wrong Answer)

# coding: utf-8
# Your code here!

# 7で割り切れる数かを検証するということは1 ~ kで割ると良い
# ただし、毎回10をかけて7を足していると計算できない範囲まで大きくなるので毎回kで割ったあまりを用いる

k = int(input())

num = 7

for i in range(1, k + 1):
    num = num * 10 + 7
    if num % k == 0:
        print(i + 1)
        exit()
    else:
        num %= k
        
print(-1)
exit()