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: Accepted)

def main():
    K = int(input())

    crawler = 7
    found = False
    i = 1

    if (K % 2 ==0) or (K % 5 == 0):
        print(-1)
    else:
        a = [0 for i in range (K+1)]
        a[0] = 7
        for i in range (1, K+1):
            a[i] = (a[i-1]*10 + 7) % K
        a[0] = a[0] % K
        for i in a:
            if i == 0:
                print(a.index(i) + 1)
                found = True
                break
        if not found:
            print(-1)
    
main()