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)

#include<bits/stdc++.h>
//#define long long ll ;
#define mod 1e+9;
#define rep for(int i=0;i<n;i++);
#define pb push_back;
#define popb pop_back;
using namespace std;
const int ma=1e6+9;
typedef long long ll;
 
int main()
{
//     #ifndef ONLINE_JUDGE
// 	freopen("input.txt", "r", stdin);
// 	freopen("output.txt", "w", stdout);
// #endif
   ios_base::sync_with_stdio(0);
    cin.tie(0);
    int k;
    cin >>k;
    ll cnt=0;
  int i;
    for( i=1;i<=k;i++)
    {
      cnt=(cnt*10+7)%k;
      if(cnt%k==0)
      {
         break;
      }
    }
    if(i==k+1)
    {
      if(cnt%k==0)
        cout << i << endl;
      else
      cout <<"-1" <<endl;
    }
    else
      cout << i << endl;
 
  }