Score : 300 points
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.
Input is given from Standard Input in the following format:
K
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
.)
101
4
None of 7, 77, and 777 is a multiple of 101, but 7777 is.
2
-1
All elements in the sequence are odd numbers; there are no multiples of 2.
999983
999982