Problem:
Score : 300 points

Problem Statement

Find the price of a product before tax such that, when the consumption tax rate is 8 percent and 10 percent, the amount of consumption tax levied on it is A yen and B yen, respectively. (Yen is the currency of Japan.)

Here, the price before tax must be a positive integer, and the amount of consumption tax is rounded down to the nearest integer.

If multiple prices satisfy the condition, print the lowest such price; if no price satisfies the condition, print -1.

Constraints

1 \leq A \leq B \leq 100

A and B are integers.

Input

Input is given from Standard Input in the following format:

A B

Output

If there is a price that satisfies the condition, print an integer representing the lowest such price; otherwise, print -1.

Sample Input 1

2 2

Sample Output 1

25

If the price of a product before tax is 25 yen, the amount of consumption tax levied on it is:

When the consumption tax rate is 8 percent: \lfloor 25 \times 0.08 \rfloor = \lfloor 2 \rfloor = 2 yen.

When the consumption tax rate is 10 percent: \lfloor 25 \times 0.1 \rfloor = \lfloor 2.5 \rfloor = 2 yen.

Thus, the price of 25 yen satisfies the condition. There are other possible prices, such as 26 yen, but print the minimum such price, 25.

Sample Input 2

8 10

Sample Output 2

100

If the price of a product before tax is 100 yen, the amount of consumption tax levied on it is:

When the consumption tax rate is 8 percent: \lfloor 100 \times 0.08 \rfloor = 8 yen.

When the consumption tax rate is 10 percent: \lfloor 100 \times 0.1 \rfloor = 10 yen.

Sample Input 3

19 99

Sample Output 3

-1

There is no price before tax satisfying this condition, so print -1.

Solution in Rust (1.15.1) (judge verdict: Accepted)

fn tax_increase() -> Result<i32, &'static str> {
    let mut input = String::new();
    std::io::stdin().read_line(&mut input)
        .map_err(|_| "input error")?;

    let ab: Vec<i32> = input.trim_right()
        .split_whitespace()
        .map(|n| n.parse::<i32>().unwrap())
        .collect();

    let a = ab[0];
    let b = ab[1];
    let mut n: f32 = 1.0;
    loop {
        let an = (n * 0.08) as i32;
        let bn = (n * 0.1) as i32;
        if an == a && bn == b {
            return Ok(n as i32);
        }
        else if an > a && bn > b {
            return Ok(-1);
        }
        n += 1.0;
    }
}

fn main() {
    println!("{}", tax_increase().unwrap());
}