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 <stdlib.h>
#include <string.h>
#include <math.h>
#include <stdio.h>
int compare(const void *a,const void *b){
    if(*(long long *)a>*(long long *)b)return 1;
    return -1;
}
int main(int argc, const char * argv[]) {
    int k;
    scanf("%d",&k);
    if(k%2==0||k%5==0){
        printf("-1");
        return 0;
    }
    int i=7,cnt=1;
    while(i){
        if(i%k==0){
            printf("%d",cnt);
            return 0;
        }
        cnt++;
        i*=10;
        i+=7;
        i%=k;
    }
    
    
    return 0;
}