Contest Duration: - (local time) (100 minutes) Back to Home
C - Repsept /

Time Limit: 2 sec / Memory Limit: 1024 MB

### 問題文

7,77,777,\ldots という数列の中に初めて K の倍数が登場するのは何項目ですか？

### 制約

• 1 \leq K \leq 10^6
• K は整数である。

K

101

### 出力例 1

4

7,77,777101 の倍数ではありませんが、7777101 の倍数です。

2

-1

999983

### 出力例 3

999982

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.)

101

### Sample Output 1

4

None of 7, 77, and 777 is a multiple of 101, but 7777 is.

2

### Sample Output 2

-1

All elements in the sequence are odd numbers; there are no multiples of 2.

999983

999982