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: Time Limit Exceeded)

#include<bits/stdc++.h>
#define mp make_pair
#define ff first
#define ss second
#define bg begin()
#define en end()
#define pb push_back
#define w(x) scanf("%d",&x);while(x--)
#define ws(x) scanf("%d",&x);getchar();while(x--)
#define rep(i,b) for(i=0;i<=b;i++)
#define ios ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define pi 2*acos(0.0)
#define endl "\n"
using namespace std;
typedef long long ll;
typedef pair<ll,ll> pll;
typedef vector<int> vi;

const int N=1e6+2;
long long  mod=1e9+9;
int t,j,cs=0,n,b,i,a;
string s;

int main()
{
    ios
        scanf("%d",&n);
        string s;

        int a=7;
        int cnt=1;
        if(n%2==0) {
            cout<<-1<<endl;
            return 0;
        }
        while(a%n!=0){
            a=a%n;
            a=a*10+7;
            cnt++;

           // cout<<a<<endl;
        }
        cout<<cnt<<endl;

}