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 <stdio.h>

int main(void){
	
	int input;			//nyuuryoku
	int input_a; 		//ああ掛け合わせた数字
	int base7 = 7;		//ああ比較変数
	int i = 1;
	
	scanf("%d",&input);
	
	if((i%2) == 0){
		printf("%d",-1);
		return -1;
	}
	
		
	while(1){
		input = input * i;

		if(input == base7) break;
		
		if(base7 < input){	
			base7 += base7 * 10;
		}
		
		i++;
	}
	
	
	printf("%d",i);
	return 0;
	
	
}