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)

#include <stdio.h>
#include <math.h>
#include <string.h>
typedef long long ll;
#define N 105
 
ll cal(ll n){
    ll t = n;
    ll p = 1,q = 1;
    while(t >= 10){
        p *= 10;
        q *= 9;
        t /= 10;
    }
     
    t = n;
    ll cnt = 0;
    while(p){
        ll num = t/p;t %= p;
        if(num == 7){
            cnt += num*q;
            --cnt;
            break;
        }
        if(num > 7) --num;
        cnt += num*q;
        p /= 10;
        q /= 9;
    }
    return n-cnt;
}
 
int main()
{
    ll n;
    while(~scanf("%lld",&n)) printf("%lld\n",cal(n));
    return 0;
}