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>
#define MAX 1000000
int main(void){
    // Your code here!
    int K,flag=1;
    scanf("%d",&K);
    int mod=7;
    for(int i=0;i<MAX;i++){
        mod=mod%K;
        if(mod==0) {
            printf("%d",i+1);
            flag =0;
            break;
        }
        else{
        mod=mod*10 +7;
        }
    }
    if(flag==1) printf("-1");
    return 0;
}