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)


// Problem : C - Repsept
// Contest : AtCoder - AtCoder Beginner Contest 174
// URL : https://atcoder.jp/contests/abc174/tasks/abc174_c
// Memory Limit : 1024 MB
// Time Limit : 2000 ms
// Powered by CP Editor (https://github.com/cpeditor/cpeditor)

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define mp make_pair
#define all(a) a.begin(),a.end()
#define sort(a) sort(all(a))
#define ff first
#define ss second
#define vi vector<int>
#define pii pair<int, int>
#define vll vector<ll>
#define pll pair<ll,ll>
#define mod (ll)1e9+7
#define FAST std::ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define repf(i,a,b) for(i=a;i<b;i++)
#define repb(i,a,b) for(i=a;i>=b;i--)
#define N 100005
int main()
{
	FAST
    int t=1;
    // cin>>t;
    while(t--)
    {
		ll x;
		cin>>x;
		if(x%2==0 || x%10==5) cout<<-1;
		else
		{
			if(x==7) cout<<1;
			else
			{
				if(x%7==0) x/=7;
				ll sum=1,rem=1;
				ll cnt=0;
				while(sum)
				{
					cnt++;
					rem=rem*10;
					rem%=x;
					sum=(sum+rem)%x;
					// rem=(rem+y)%x;
					
				}
				cout<<cnt+1;
			}
		}
    }
    return 0;
}