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: Time Limit Exceeded)

#C
# 7,77,777･･･=7*(1,11,111･･･)
# 7*(10^i)=7*(10^i-1)/10-1 = 7*(10^i-1)/9 がkで割れる
# 10^iを(9k,7の倍数だったら9k/7)で割ってあまりが１だったら良い
import sys
k=int(input())
if k%7==0:
    k//=7
k*=9
a=10%k
for i in range(k*9):
    a=a%k
    if a==1:
        print(i+1)
        sys.exit()
    a*=10
print(-1)