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)

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>

int main(){
    int k;
    int i;
    int flag = 0;
    int s[1000000];

    scanf("%d", &k);

    for(i = 0;i < k;i++){
        if(i == 0) s[i] = 7;
        if(i != 0) s[i] = s[i - 1] * 10 + 7;

        if(s[i] % k == 0){
            printf("%d", i + 1);
            flag = 1;
            break;
        }
    }

    if(flag == 0) puts("-1");

    return 0;
}