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>
#include <stdio.h>
typedef long long int LL;
#define fr(i,p,n) for(LL i=p;i<n;i++)
#define fr1(i,p,n) for(LL i=p;i>=n;i--)
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define all(v) v.begin(),v.end()
#define PI 3.14159265358979323846
#define MOD 1000000007
#define MOD1 998244353
#define INF 1e18
#define precise cout << std::setprecision(10) << std::fixed;

using namespace std;

int main()
{
        LL n;
        cin>>n;
        if(n%2==0){
            cout<<-1<<endl;
        }
        else{ 
            map<int,int> mp;
            LL mod=0;
            LL cnt=1;
           while(1){
               mod = mod * 10 + 7;
               mod = mod % n;
               if(mp[mod]>0) break;
               mp[mod]++;
              if(mod==0){
                 cout<<cnt<<endl;
                 break; 
              }
              cnt++;     
           }
        }
    return 0;
}