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>
int main(void)
{
  int a, non_taxed_price_a, max_non_taxed_price_a, min_non_taxed_price_a,
    b, non_taxed_price_b, max_non_taxed_price_b, min_non_taxed_price_b,
    i, ans;

  // 標準入力からの値取得
  scanf("%d %d", &a, &b);

  // 計算
  max_non_taxed_price_a = (int)((float)a / 8.0 * 108.0);
  for (i = max_non_taxed_price_a + 1; ; i++) {
    if (((int)((float)i / 8.0 * 108.0)) != a) {
      max_non_taxed_price_a = i - 1;
      break;
    }
  }
  min_non_taxed_price_a = (int)((float)a / 8.0 * 108.0);
  for (i = min_non_taxed_price_a - 1; ; i--) {
    if (((int)((float)i / 8.0 * 108.0)) != a) {
      min_non_taxed_price_a = i + 1;
      break;
    }
  }

  max_non_taxed_price_b = (int)((float)b / 10.0 * 110.0);
  for (i = max_non_taxed_price_b + 1; ; i++) {
    if (((int)((float)i / 10.0 * 110.0)) != b) {
      max_non_taxed_price_b = i - 1;
      break;
    }
  }
  min_non_taxed_price_b = (int)((float)b / 10.0 * 110.0);
  for (i = min_non_taxed_price_b - 1; ; i--) {
    if (((int)((float)i / 10.0 * 110.0)) != b) {
      min_non_taxed_price_b = i + 1;
      break;
    }
  }

  ans = -1;
  if (min_non_taxed_price_b <= max_non_taxed_price_a) {
    ans = min_non_taxed_price_b;
  } else if (min_non_taxed_price_a <= max_non_taxed_price_b) {
    ans = min_non_taxed_price_a;
  }

  // 出力
  printf("%d\n", ans);
  return 0;
}