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 JavaScript (Node.js 12.16.1) (judge verdict: Accepted)

function Main(input) {
  input=input.split("\n");
  var target=input[0]-0;
  target*=9;
  if(target%7===0){
    target/=7;
  }
  var array=new Array(target);
  array.fill(false);
  var num=1;
  var counter=0;
  while(true){
    counter++;
    num=(num*10)%target;
    if(array[num]){
      console.log(-1);
      return;
    }
    if(num===1){
      console.log(counter);
      return;
    }
    array[num]=true;
  }
}


//*この行以降は編集しないでください（標準入出力から一度に読み込み、Mainを呼び出します）
Main(require("fs").readFileSync("/dev/stdin", "utf8"));