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<bits/stdc++.h>
#define pb push_back
#define pf push_front
#define clr(x) memset(x, 0, sizeof(x))
#define all(a) a.begin(),a.end()
#define forn(i, a,b) for(int i = int(a); i < int(b); ++i)
#define forn_r(i, b, a) for(int i = int(b); i > int(a); i--)
#define trav(a,x) for (auto& a : x)
#define printArray(array, length) for(int i = 0; i < length; i++) cout<< array[i] << (i == length - 1 ? '\n' : ' '); 
#define print(x) cout << x << '\n'
#define print2(x, y) cout << x << ' ' << y << '\n'
#define debug(x) cout << #x << "=" << x << endl
#define debug2(x, y) cout << #x << "=" << x << "," << #y << "=" << y << endl
template <typename T> bool chmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template <typename T> bool chmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; }

using namespace std;
typedef long long ll; 
const int INF = 0x3f3f3f3f;
const ll LNF  = 0x3f3f3f3f3f3f;
inline int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
inline ll  gcd(ll  a, ll  b) { return b ? gcd(b, a % b) : a; }
inline int lcm(int a, int b) { return a * b / gcd(a, b); }



int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int t =1;
    //cin>>t;
    while(t--){
    	int n;
    	cin>>n;
    	int count=0;
    	ll rem = 0; 
  		//if(n==1 || n==7) {print(1);return 0;}
     	if(n%2==0 || n%5==0){print(-1); return 0 ;}
     	
    	while (rem != 0) { 
  
        	rem = (rem * 10 + 7) % n; 
        	count++; 
       }	
       print(count+1);
       	 
    }
    return 0;
}