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)

// C++ implementation of the approach 
#include <bits/stdc++.h> 
using namespace std; 

// Function to return length 
// of the resulatant number 
int numLen(int K) 
{ 

	// If K is a multiple of 2 or 5 
	if (K % 2 == 0 || K % 5 == 0) 
		return -1; 

	int number = 0; 

	int len = 1; 

	for (len = 1; len <= K; len++) { 

		// Instead of generating all possible numbers 
		// 1, 11, 111, 111, ..., K 1's 
		// Take remainder with K 
		number = (number * 10 + 1) % K; 

		// If number is divisible by k 
		// then remainder will be 0 
		if (number == 0) 
			return len; 
	} 

	return -1; 
} 

// Driver code 
int main() 
{ 

	int k;
	cin>>k;
	if(k%7==0)
	k=k/7;
	cout << numLen(k); 

	return 0; 
}