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 pb push_back
#define mp make_pair
#define fi first
#define se second
#define sz(a) (a).size() 
#define all(c) (c).begin(),(c).end()
#define rep(i,n) for(int i=0;i<n;i++)
#define forn(i,n) for(int i=1;i<=n;i++)
#define ford(i,n) for(int i=n;i>=0;i--) 
#define REP(i,a,n) for(int i=a;i<n;i++)
#define foreach(itr,c) for(__typeof((c).begin(),(c).end())itr=c.begin();itr!=c.end();itr++) 
#define fill(a,b) memset(a,b,sizeof(a))
#define re return
#define INF 1e9
#define LINF 1e18
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pi;
typedef vector<int> vi;
typedef vector<pi > vpi; 
int main(){
	int k;
	cin>>k;
	ll num=0;
	map<ll,bool> m;
	for(int i=1;;i++){
		num=num*10+7;
		num=num%k;
		if(num==0){
			cout<<i;
			break;
		}
		else if(m[num]){
			cout<<-1;
			break;
		}
		else{
			m[num]=1;
		}
	} 
	re 0;
}