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 <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <math.h>

//#define MOD (int)(1e5 + 7)
#define MOD (100007)

static inline void done(const char *s)
{
	puts(s);
	exit(0);
}

#define yes() done("Yes");
#define no() done("No");
#define invalid() done("-1");

static int comp(const void *a, const void *b)
{
	int *pa = (int *)a;
	int *pb = (int *)b;
	return *pa < *pb;
}

static inline int *readNint(int n)
{
	int *a = calloc(sizeof(int), n);
	for (int i = 0; i < n; i++)
		scanf("%d", &a[i]);
	return a;
}

static inline long *readNlong(int n)
{
	long *a = calloc(sizeof(long), n);
	for (int i = 0; i < n; i++)
		scanf("%ld", &a[i]);
	return a;
}

int main(int argc, char **argv)
{
	int A, B;
	scanf("%d%d", &A, &B);
	for (int x = B * 10; x < B * 20; x++) {
		int a = (x * 8) / 100;
		int b = x / 10;
		fprintf(stderr, "%d %d %d\n", x, a, b);
		if (a == A && b == B) {
			printf("%d\n", x);
			return 0;
		}
	}
	printf("-1\n");
	return 0;
}