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: Accepted)

  //shan61916
#include <bits/stdc++.h>
  using namespace std;
typedef   long long ll;
typedef   unsigned long long ull ;
typedef   double dll ;

#define   mp make_pair
#define   pb push_back
#define   ff first 
#define   ss second
#define   IOS ios::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define   endl "\n" 
#define   pll pair<ll, ll>
#define   all(x) x.begin(), x.end()
#define   vll vector<ll> 

const ll inf = (ll)(1e17 + 17);
const ll mod = (ll)(1e9 + 7);


int main(){
 IOS
#ifdef SHAN
    freopen("input.txt" , "r" , stdin);  
#endif
  ll n;
  cin >> n;
  if(n%2 == 0 or n%5 == 0) {
    cout << -1;
    return 0;
  }
  ll rem = 7;
  ll ct = 1;
  for(ll i = 0; i < (ll)1.5e7; i++) {
    if(rem%n == 0) {
      cout << ct << endl;
      return 0;
    }
    rem*=10;
    rem+= 7;
    rem%=n;
    ct++;
  }
  cout << -1 << endl;
  return 0;
} //good night.