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: Time Limit Exceeded)

#include <iostream>
#include <stdio.h>

#include <vector>
#include <cctype>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <string>

using namespace std;


int main()
{
    long long k;
    cin >> k;

    //偶数は排除
    if (k % 2 == 0 || k%5==0) {
        cout << -1 << endl;
        return 0;
    }
    
    long long count = 0;
    long long i = 1;
    long long number = 7;
    while (1) {
        if (number % k == 0) {
            count = i;
            break;
        }
        else {
            number = number * 10+ 7;
            i++;
        }

    }

    cout << count << endl;

    return 0;
}