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 _USE_MATH_DEFINES
#include <math.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <string.h>


int L_in;

int main(int argc, char* argv[]){
    int i,j,now,ten,flag,temp;
    //long int tenal;
    scanf("%d",&L_in);
    now = 7;
    ten = 7;
    flag=0;
    int small10,start;
    //for(i=0;i<=6;i++){
    //    if(ten>=L_in){
    //        small10 = ten;
    //        start = i;
    //        break;
    //    }
    //    ten *=10;
    //}

    //for(i=start;i<=10000;i++){
    for(i=1;i<=100000000;i++){
        temp = now % L_in;
        if(temp == 0){
            printf("%d",i);
            flag=1;
            break;
        }
        ten *= 10;
        ten = ten % L_in;
        now = temp + ten;
    }

    if(flag==0){
        printf("-1");
    }
    return 0;
}