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: Accepted)

#include<stdio.h>

int main (void){
  int a,b,c,d = 0;

  scanf("%d %d",&a,&b);

  if(a % 2 == 0){
    for(int i = 0 ; i < ((a + 1) * 125 / 10 ) - (a * 125 / 10) + 1; i++){
      c = a * 125 / 10 + i;
      d = c / 10;
      if(b == d){
        printf("%d\n",c);
        return 0;
      }
    }
  }else{
    for(int i = 0 ; i < ((a + 1) * 125 / 10 ) - (a * 125 / 10) -1; i++){
      c = a * 125 / 10 + 1 + i;
      d = c / 10;
      if(b == d){
        printf("%d\n",c);
        return 0;
      }
    }
  }
  printf("-1\n");
  return 0;
}