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: Wrong Answer)

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    int K;
    int S[1000000];
    cin >> K;
    S[0] = 7;
    for (int i = 1; i <= K; i++)
    {
        S[i] = (S[i - 1] * 10 + 7) % K;
    }

    for (int i = 0; i <= K; i++)
    {
        if (S[i] == 0)
        {
            cout << i + 1 << endl;
            return 0;
        }
    }

    cout << "-1" << endl;
}