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 C (GCC 9.2.1) (judge verdict: Accepted)

#include<stdio.h>
int main()
{
	int a,b=0,c=0,cn=1;
	scanf("%d",&a);
	if(a%2==0){
		printf("-1\n");
	}
	else {
		b=7%a;
		while(1){
			if(cn>100000000){
				printf("-1\n");
				break;
			}
			if(b!=0){
			cn++;
			c=(b*10)+7;
			b=c%a;
			}
			else {
				printf("%d\n",cn);
				break;
			}
		}
	}
	return 0;
}