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: Accepted)

#include <bits/stdc++.h>
using namespace std;
#define endl "\n"
#define fo for(int i=0;i<n;i++)
#define clear cin.clear();cin.ignore(numeric_limits<streamsize>::max(), '\n');
#define loopSolve int t; cin>>t; while(t--){solve();}
#define rep(i, n)    for(int i = 0; i < (n); ++i)
#define repA(i, a, n)  for(int i = a; i <= (n); ++i)
#define repD(i, a, n)  for(int i = a; i >= (n); --i)
#define trav(a, x) for(auto& a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()
#define fill(a)  memset(a, 0, sizeof (a))
#define fst first
#define snd second
#define mp make_pair
#define pb push_back
typedef long double ld;
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

//INT_MAX         2,147,483,647                       <10^10
//U_INT_MAX       4,294,967,295                       <10^10
//LONG_LONG_MAX   9,223,372,036,854,775,807           <10^18
//U_LONG_LONG_MAX 18,446,744,073,709,551,615          <10^18
//ll power(int a, int b){
//    return (ll)(pow(a,b)+0.5);
//}

vector<int> gV(int n){
    vector<int> v(n);
    fo { cin>>v[i];  }
    return v;
}

int* gA(int n){
    int* arr = new int[n];
    fo cin>>arr[i];
    return arr;
}



void solve(){
    int k;
    cin>>k;
    map<int,bool> vis;
    int val=7,pos=1;
    while(1){
        if(val%k==0){
            cout<<pos<<endl;
            return;
        }else{
            if(vis[val%k]){
                cout<<-1<<endl;
                return;
            }
            vis[val%k]=true;
            val=(10*val+7)%k;
            pos++;
        }
    }
}


int main() {
	ios_base::sync_with_stdio(false);
    std::cin.tie(NULL);
    std::cout.tie(NULL);

    solve();
    //loopSolve;

	return 0;
}