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 <ext/pb_ds/assoc_container.hpp>
 
using namespace __gnu_pbds;
using namespace std;
 
typedef long long int ll;
typedef unsigned long long int sll;
typedef long double ld;
#define A 1000000007
#define D 100000000000000ll
#define B 998244353ll
#define C 1000000000000000000ll
#define M 4000
#define FAST ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define oset tree<ll, null_type,less_equal<ll>, rb_tree_tag,tree_order_statistics_node_update> 
#define pb push_back
#define pf push_front
#define pob pop_back
#define pof pop_front
#define mxe(v) *max_element(v.begin(),v.end())
#define mne(v) *min_element(v.begin(),v.end())
#define bs binary_search
#define lb lower_bound
#define ub upper_bound
#define ve vector
#define br break
#define PI acos(-1)
#define subt cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC << "ms\n" 

int main() 
{
    FAST;
    ll k,p,co;
    cin>>k;
    p=1%k;
    co=1;
    if(k%2==0 || k%5==0)
    {
        cout<<-1;
        return 0;
    }
    if(k%7==0)
        k=k/7;
    while(co<5000000 && p!=0)
    {
        p=((p*10ll)+1)%k;
        co++;
    }
    cout<<co;
    subt;
    return 0;
}