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 <cstring>
#include <stdlib.h>
#include <vector>
#include <algorithm>
#include <cmath>
#include <stack>
#include <queue>
#include <math.h>
#include <string>
#include <map>
#include <cstdlib>
#include <sstream>
#include <bitset>
using namespace std;

typedef long long ll;
typedef pair<ll,ll> P;


int main()
{
    ll K;
    cin >> K;
    
    vector<int> remain(K,-1);
    ll tmp=7,cnt=1,ans=-1;
    while(true){
        tmp%=K;
        if(tmp==0){
            ans=cnt;
            break;
        }else if(remain[tmp]!=-1){
            break;
        }
        remain[tmp]=1;
        cnt++;
        tmp=tmp*10+7;
    }
    

    cout << ans << endl;
    


    return 0;
}