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 all(v) (v).begin(), (v).end()
#define lp(i, n) for (int i = 0; i < (n) ; ++i)
#define pr1(x) cout<<"[" << #x << ": " << x << "] \n";
#define pr2(x, y) cout<<"[" << #x << ": " << x <<", "<< #y << ": " << y <<"] \n";
#define mod 1000000007
#define int long long
#define sz(v) (int)(v).size()

void solve() {
        int n; cin >> n;
        int s= 7;
        for (int i = 1; i<= 1e6; i++) {
                if (s% n== 0) {
                        cout << i<< "\n";
                        return;
                }
                s%= n;
                s= s* 10+ 7;
        }
        cout << "-1\n";
}

int32_t main(){
ios::sync_with_stdio(0), cin.tie(NULL), cout.tie(NULL);
        int t = 1;
        //cin >> t;
        while ( t-- ) {
                solve();
        }
return 0;
}