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>
using namespace std;
#define ll long long
#define pb push_back
#define all(x)  x.begin(),x.end()
#define vi vector<int>
#define vll vector<ll>
#define print(x) for(auto it=x.begin();it!=x.end();it++) cout<<*it<<' '; cout<<'\n';
#define debug(a,b,c) cout << a << " " << b << " " << c << endl;
#define in(x,n) for(int e=0;e<n;e++){int y;cin>>y;x.pb(y);}
#define inl(x,n) for(int e=0;e<n;e++){ll y;cin>>y;x.pb(y);}
#define lower(sl)  transform(sl.begin(), sl.end(), sl.begin(), ::tolower); 
#define endl "\n";
#define pi pair<int,int>
#define vpi vector<pair<int,int>>
#define vvi vector<vector<int>>
 

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	//code here
    ll k; cin >> k;
	ll curr = 7, prev = 7;
	ll res = 1;
	if(k%2==0 or k%5==0){
		cout << -1 << endl;
		return 0;
	}
	for(int i=0;i<k;i++){
		if(curr%k==0) break;
		prev = (prev*10) % k;
		curr = (curr+prev) % k;
		res++;
	}
	cout << res << endl;

}