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: Wrong Answer)

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
#define rep(i,n) for(int i=0;i<n;i++)
#define rept(i,n) for(int i=n-1;i>=0;i--)
#define FOR(i,m,n) for(int i=m;i<n;i++)
#define all(v) v.bigin(),v.end()
#define MAX(a,b) a=a>b?a:b
#define MIN(a,b) a=a<b?a:b
#define FAST ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
int main(){
    FAST;
    ll k;
    ll s=0;
    ll ans=-1;
    cin>>k;
    ll n=7000000;
    rep(i,n){
        s+=7*pow(10,i);
        if(s%k==0){
            ans=i+1;
            break;
        }
    }
    cout<<ans;
    
}