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)

//                               //
    // author : samars_diary //
    // 17-09-2020 │ 17:10:23 //
//                               //

#include <iostream>
#include <cmath>
using namespace std;

void solve(){
    long long int a;
    cin>>a;
    int val(7);
    for(int i=1; i<10000000; i++){
        if(val==0){
            cout<<i;
            return;
        }
        val=(val*10+7)%a;
    }
    cout<<-1;
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);

    //#ifndef ONLINE_JUDGE
        //freopen("input.txt", "r", stdin);
        //freopen("output.txt", "w", stdout);
    //#endif

    int t = 1;
    while(t--){
        solve();
    }

    return 0;
}