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>
using namespace std;
 
 
int main(){
  long long k;
  cin >> k;
  if(k % 2 == 0){
    cout << "-1" << endl;
  }
  else{
    long long x = 7;
    long long ans = 0;
    
    while(ans <= 999983){
      x = x % k;
      ans ++;
      if(x== 0){
        break;
      }
      x *= 10;
      x += 7;
    }
    if(ans == 999983){
      cout << "-1" << endl;
    }
    else{
      cout << ans << endl;
    }
  }
}