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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>

#define TAX_8 0.08
#define TAX_10 0.10

int main(void) {
    int a, b;
    scanf("%d %d", &a, &b);

    int fee_a = (float) a / (float) TAX_8, fee_b = (float) b / (float) TAX_10;
    // printf("%d %d\n", fee_a, fee_b);
    int flag_a, flag_b;
    if ((int) ((float) fee_a * (float) TAX_10) == b) {
        flag_a = 1;
    }
    if ((int) ((float) fee_b * (float) TAX_8) == a) {
        flag_b = 1;
    }
    if (fee_a < 0 || fee_b < 0) {
        printf("-1\n");
    } else if (flag_a && flag_b) {
        if (fee_a < fee_b) {
            printf("%d\n", fee_a);
        } else {
            printf("%d\n", fee_b);
        }
    } else if (flag_a && !flag_b) {
        printf("%d\n", fee_a);
    } else if (!flag_a && flag_b) {
        printf("%d\n", fee_b);
    } else {
        printf("-1\n");
    }

    return 0;
}