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>
	#include <cstdio>
	#include <cstring>
	#include <cmath>
	#include <cstring>
	#include <chrono>
	#include <complex>
	#define endl "\n"	
	typedef long long LL;
	#define ll  unsigned long long int
	#define vi vector<int>
	#define vll vector<ll>
	#define vvi vector < vi >
	#define pii pair<int,int>
	#define pll pair<long long, long long>
	//#define mod 1000000007
	#define mod2 998244353
	#define inf 1000000000000000001;
	#define all(c) c.begin(),c.end()
	#define sz(v) ((ll)(v).size())
	#define mp(x,y) make_pair(x,y)
	#define mem(a,val) memset(a,val,sizeof(a))
	#define eb emplace_back
	#define pb push_back
	#define f first
	#define s second
	#define dbg(a) cout<<#a<<" --> "<<(a)<<"\n";
	#define forn(i,n) for (ll i=0; i<(n); ++i)
	#define fornd(i,n) for (ll i=(n)-1; i>=0; --i)	
	#define forab(i,a,b) for (ll i=(a); i<=(b); ++i)
	#define read(a) ll a; cin >> a;
	#define reads(s) string s; cin >> s;
	#define readb(a, b) ll a, b; cin >> a >> b;
	#define readc(a, b, c) ll a, b, c; cin >> a >> b >> c;
	#define readarr(a, n) int a[(n) + 1] = {}; forab(i, 0, (n-1)) {cin >> a[i];}
	#define readmat(a, n, m) int a[n + 1][m + 1] = {}; forab(i, 1, n) {forab(j, 1, m) cin >> a[i][j];}
	#define readv(A,n) vll A(n,0); forn(i,n) cin>>A[i]; 
	#define print(a) cout << a << endl;
	#define printarr(a, n) forab (i, 1, n) cout << a[i] << " "; cout << endl;
	#define printv(v) for (int i: v) cout << i << " "; cout << endl;
	#define printmat(a, n, m) forab(i, 1, n) {forab (j, 1, m) cout << a[i][j] << " "; cout << endl;}
	 
	#define fast_io ios_base::sync_with_stdio(false),cin.tie(NULL),cout.tie(NULL)
	using namespace std;
	
	void solve()
	{
		ll k;
		cin>>k;
		set<ll> pq;
		ll er=7%k;
		ll i=1;
		while(er!=0)
		{
			 er=(10*er+7)%k;
				i++;
			// if(temp%k==1)
			// {
			// 	cout<<i<<endl;
			// 	return;
			// }
			if(pq.count(er))
			{
				cout<<"-1"<<endl;
				return;
			}

		}
		cout<<i<<endl;
		//cout<<"-1"<<endl;

	}
	int main()
	{	
		#ifndef ONLINE_JUDGE
		freopen("input.txt","r",stdin);
		freopen("output.txt","w",stdout);
		#endif
		fast_io;
		int T=1;
		//cin>>T;
		// cin.ignore(); must be there when using getline(cin, s)
		while(T--)
		{
			solve();
		}
		return 0;
	}