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 lli long long int
#define MOD 1000000007
#define KING 1000000002
#define queen 1000002
#define fi first
#define se second
#define se second
#define lsb(i) (i & -i)
#define Pi 3.141592653589793238
#define nl cout<<'\n'
#define TEST cout<<"TEST",nl
#define all(a) a.begin(), a.end()
#define remax(a, b) (a = ((a<b) ? b : a))
#define remin(a, b) (a = ((a<b) ? a : b))
#define pr pair<lli,lli>
#define pb push_back
#define eb emplace_back
#define precise(a) cout<<fixed<<setprecision(a)
#define mp make_pair
#define vi vector<lli>
#define vpi vector<pr> 
#define P pair<lli,pr>
#define fastIO ios_base::sync_with_stdio(false); cin.tie(NULL)
#define NA(i,s,n) for(lli i=s;i<n;i++)
using namespace std;

lli power(lli x,lli y,lli p = (lli)(1e13)) { 
	lli res = 1;	 
	x = x % p; 
	while (y > 0) 
	{ 
		if (y & 1) 
			res = (res*x) % p; 
		y = y>>1; 
		x = (x*x) % p; 
	} 
	return res; 
}

long double dst(pair<lli,lli> p) {
    return sqrt(p.fi*p.fi + p.se*p.se);
}

void solve(){
    lli k; cin >> k;
    if(k==7) {
        cout << 1 << '\n';
    } else if(k%2==0) {
        cout << -1 << '\n';
    } else {
        lli r = 0, md = 0;
        bool fg = 0;
        NA(i,0,k) {
            md*=10, md=(md+7)%k;
            if(md%k==0) {cout << (i+1) << '\n'; fg = 1; break;}
        }
        if(!fg) cout << -1 << '\n';
    }
    return;
}


int main(){
    fastIO;
    lli t = 1;
    // cin >> t;
    NA(i,0,t){ 
		// cout << "Case #" << i+1 << ": \n";
		solve();
	}
	return 0;
}