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: Runtime Error)

#include <cstdio>
#include <cstring>
#include <queue>
#include <iostream>
#include<bits/stdc++.h>
typedef long long int ll;
using namespace std;
int f;

ll division(ll n)
{
    //char ans[MAX_N];
   ll con=0;
    bool flag = true;
    ll k = 0,s = 0,t = 0;
    ll g=10000000;
    while(g--)
    {
        ll it=s;
        t = s*10 + 7;
        con++;
        if(t/n>0 || t == 0)
        {

            s = t%n;
            flag = false;
        }
        else
        {
            s = t;

        }
        if(!flag){if(it==s){f=0;return con;}}
        if(!flag){if(s==0){f=1;return con;}}
    }
    f=0;
}

int main()
{

   ll k;
   cin>>k;
   ll c=division(k);
   if(f==1||c==1)printf("%lld\n",c);
   else printf("-1\n");
    return 0;
}