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: Runtime Error)

#include<iostream>
using namespace std;
int main()
{
  int n,k;
  long long int a[n];
  cin>>n>>k;
  int count=0;
  a[1]=7;
  for( int i=2;i<=n;i++)
     a[i]=((a[i-1]*10)+7);
  for( int i=1;i<=n;i++)
  {
    if(a[i]%k==0)
    {
      count++;
      cout<<a[i];
      break;
    }
  }
  if(count==0)
    cout<<"-1";
  return 0;
}