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>
#include <stdbool.h>
int cnt=0;
int main(){
  int k;
  long long int n=10000000000;
  scanf("%d",&k);
  for(long long int i=1;i<n;i++){
    //printf("%d\n",i );
    if(chkAllSeven(k*i) ){
      //printf("%lld <- i\n",i );
      //printf("%lld <- k*i \n",k*i );
      printf("%d\n",cnt );
      return 0;
    }
  }
  printf("-1\n");
}
int chkAllSeven(long long int n){
  cnt=0;
  while(n!=0){
    int a;
    a=n%10;
    cnt+=1;
    if(a!=7)
    return 0;
    n=n/10;
  }
  return 1;
}