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 <iostream>
#include <string>
#include <math.h>
#include <vector>
#include <algorithm>
#include <iomanip>
#include <set>
#include <queue>
#include <deque>
#include <map>
#include <stack>
#include <cmath>
using namespace std;

#define mod 1000000007
#define ten5 100005
#define ten52 200005
#define ten6 1000005
#define PI 3.1415926
#define pb(x) push_back(x)
#define all(x) x.begin(),x.end()
#define mkpr(x1,x2) make_pair(x1,x2)
typedef long long int ll;


//stack<char> stk;
//set<ll> sll;
//set<pair<ll,ll>> spll;
//map<string,ll> mp;
//map<pair<ll,ll>,ll>::iterator iter;
//map<ll,ll> mp;
//deque<ll> deq;
//vector<ll> vll;
ll num[ten5],pp[ten52],mm[ten52];
//priority_queue<ll> pq;          //decreasing

int main(void)
{
    ll m,n,i,j,k=1;
    cin>>n;
    if(n%2==0 || n==5) cout<<-1;
    else
    {
        j=7%n;
        while(1)
        {
            j=j*10+7;
            j%=n;
            k++;
            if(j==0) break;
        }
        cout<<k;
    }

    return 0;
}