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)

k = int(input())
if k%2==0 or k%5==0:
    print(-1)
    exit()
    
def so(n):
  for i in range(2,int(n**0.5)+1):
    if n%i==0:
      return False
  else:
    return True
    
t = 50000
if k%7==0:
  k//= 7
l = len(str(k))
s = int(str(1)*l)
ind = l
while t!=0 :
    if s%k==0:
        print(ind)
        exit()
    else:
        s = s*10+1
        ind += 1
    t -=1
if so(k)==True:
  print(k-1)
  exit()