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: Wrong Answer)


#include<stdio.h>
int main()
{
	int i,K,p = -1,ans;
	int b[100000];
	b[0] = 0;
	scanf("%d", &K);
	for (i = 1; i < 100001; i++) {
		b[i] = 10 * b[i - 1] + 7;
	}
	for (i = 1; i < 100001; i++) {
		if (b[i] % K == 0) {
			p = 1;
			ans = i;
		}
	}
	if (p == -1) {
		printf("%d", p);
	}
	else {
		printf("%d", ans);
	}
}