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: Accepted)

#include <iostream> 
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <map>
using namespace std;
long long x,y,n,d;
int ans = 0;
bool vis[1010101];
int main() {
	int k;
	scanf("%d",&k);
	int now = 7%k,ans = 1;
	while (now) {
		if (vis[now]) {
			printf("-1");
			return 0;
		}
		vis[now] = 1;
		now = (now*10+7)%k;
		ans++;
	}
	printf("%d\n",ans);
	return 0;
}
/*
4
8 3
2 3 2 1 3 3 2 1
6 3
2 3 2 3 2 3
8 3
2 3 2 1 3 3 2 1
12 4
1 2 3 4 4 3 2 1 2 4 1 3

*/