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(void){
	int num;
	int spl;
	int ans=1;
	scanf("%d",&num);
	
	if(num%2==0) printf("-1\n");
	else if(num%5==0) printf("-1");
	//else if(num==1)  printf("-1");
	else {
       spl=7%num;
	while(1){
		if(spl==0){
			printf("%d\n",ans);
			break;
		}
       ans+=1;
	   spl=spl*10+7%num;
	   if(spl>=num)
	     spl=spl%num;
	}
    }
	return 0;
}