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>
#include <stdlib.h>
#include <math.h>

int main(){
    int k;
    long long int list[1000000];
    scanf("%d",&k);
    list[0] = 7%k;
    for(int i=1;i<k+1;i++){
        list[i] = list[i-1]+(int)7*pow(10,i);
        list[i] %= k;
        if (list[i] == 0){
            printf("%d\n",i+1);
            exit(0);
        }
    }/*
    for(int i=0;i<k;i++){
        printf("%lld\n",list[i]);
    }
    */
   printf("-1\n");
    return 0;
}