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)

#pragma GCC optimize(2)
#include<bits/stdc++.h> 
using namespace std;
#define ll long long
#define endl "\n"
const int mod=1e9+7;
const int MAX=1e6+7;
ll a[10]={7,77,777,7777,77777,777777,7777777,77777777,77777777,777777777}; 

int main(){
    ios_base::sync_with_stdio(0);cin.tie(0);
  	ll n;cin>>n;
  	if(n%2==0){
  		cout<<-1;return 0;
	}
  	for(int i=0;i<9;i++)
  	if(n==a[i]){
  		cout<<i+1;return 0;
	}
	ll cnt=7,ans=0;
	for(int i=0;i<30;i++){
		if(cnt%n==0){
			ans=i+1;break;
		}
		cnt=cnt*10+7;
	}
   if(ans==0)cout<<-1;
   else cout<<ans;
   return 0;
}