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: Accepted)

#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <queue>
#include <stack>
#include <math.h>
#include <string>
#include <limits.h>
#include <iomanip>
#include <deque>
#include <bitset>
#include <iterator>
#include <list>
#include <set>
#include <bitset>
#include <unordered_map>
#include <string.h>
#define fastIo                        \
    ios_base::sync_with_stdio(false); \
    cin.tie(NULL)
#define ll long long
#define ff first
#define ss second
#define pb push_back
#define ppb pop_back
#define mp make_pair
#define MOD 1000000007

using namespace std;
int main()
{
    fastIo;
    
    ll n;
    cin>>n;
    if(n%2==0 || n%5==0)
        {
            cout<<-1<<endl;
            return 0;
        }
    ll ans=7;
    ll c=1;

    bool found = false; 
    while(true)
    {
        if(c>n)
            break;
        
        ans%=n;
        if(ans==0)
            {
                found=true;
                break;
            }
        ans = ans*10+7;
        c++;
    }
    if(found)
        cout<<c<<endl;
    else
    {
        cout<<-1<<endl;
    }
    


    return 0;
}