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 <bits/stdc++.h>
#define ll long long
#define pub push_back
#define mp make_pair
#define MAX 
#define ull unsigned ll
 
using namespace std;

ifstream fin("input.txt");
string str;


int main()
{
  ios :: sync_with_stdio(false);
  
  ll k ; 
  cin >> k;
  
  ll n = 7 ;
  ll cnt  = 1 ;
  
  while ( n % k && cnt <= 1e7 )
  {
	   cnt+=  1 ;
	   n = ( n * 10 ) + 7  ; 
  } 
 
  cout<<n<<endl;
  if (n % k)
  cout<<-1 ;
  else
  cout<<cnt ;
  cout<<endl;
}