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)

/*
    Author - Param Kothari
    Ah shit, here we go again
*/

#include <bits/stdc++.h>
 
using namespace std;

#define IOS ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define pb push_back
#define mk make_pair

typedef long long ll;
typedef long double ld;

void solve(){
    int k = 0;
    cin >> k;
    int curr = 7;
    int res = 1;
    if(__gcd(k, 10) != 1){
        cout << -1 << "\n";
        return;
    }
    while(1){
        if(curr % k == 0){
            break;
        }
        curr = (((curr * 10) % k) + 7) % k;
        res++;
    }
    cout << res << "\n";
    return;
}

int main(){
    IOS;
    int t = 1;
    // cin >> t;
    for(int i = 1; i <= t; i++){
        solve();
    }
    return 0;
}