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: Time Limit Exceeded)

#include <bits/stdc++.h>
using namespace std;

int main()
{
 int K;
  cin >> K;
  int a = 0;
  int c = 1;
  int q = K % 2;
  int w = K % 5;
  if ( q == 0  ) {
    cout << -1 << endl;
                }
  
  else if ( w == 0 ){
    cout << -1 << endl;
                    }
  
  else {
    
  while ( true ){
    a += 1;
   int b = a*7;
     if ( b % K == 0 ){
       cout << c << endl;
       break;
                       }
    else {
      a *= 10;
      c += 1;
         }
    
                 }
    
        }
  
}