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 Ruby (2.7.1) (judge verdict: Time Limit Exceeded)

k = gets.chomp!.to_i
LS = []
def sevens(s, k, count)
    if s%k == 0
        return count
    else
        LS << s%k
        
        
        count += 1
        s = "7" * count
        s = s.to_i
        sevens(s, k, count)
    end
end

# countを事前に決めてしまう

def make_s(s, k)
    if s < k
        s = (s.to_s + "7").to_i
        make_s(s, k)
    else
        return s
    end
end

s = 7
s = make_s(s, k)
count = s.to_s.length



if k%2 == 0
    puts "-1"
else  
    puts sevens(s, k, count)
end