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++ (Clang 10.0.0) (judge verdict: Wrong Answer)

/*  -*- coding: utf-8 -*-
 *
 * c.cc: C - Repsept
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_K = 1000000;

/* typedef */

/* global variables */

bool used[MAX_K];

/* subroutines */

/* main */

int main() {
  int k;
  scanf("%d", &k);

  int c = 1;
  for (int r = 7; r > 0; c++) {
    r = (r * 10 + 7) % k;
    if (used[r]) {
      puts("-1");
      return 0;
    }
    used[r] = true;
  }

  printf("%d\n", c);
  return 0;
}