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>
using namespace std;
#define fo(i,n) for(int i=0; i<n; i++)
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define MOD 1000000007
void code(){
    long long k,i;
    scanf("%lld", &k);

    if(!(k&1) || k%5==0){
        printf("-1");
        return;
    }

    long long ans = 1;
    for(i=1%k; ; i=(i*10+1)%k){
        if(i==0) {
            printf("%lld", ans);
            return;
        }
        ans++;
    }
    
}


int main(){
    IOS;
    #ifndef ONLINE_JUDGE
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    #endif
    code();
    return 0;
}