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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
#define fast ios_base::sync_with_stdio(0);cin.tie(0)
#define debug freopen("input", "r", stdin);freopen("output", "w", stdout)
#define endl '\n'
#define all(var) var.begin(), var.end()
int const MOD = 1e9+7;
typedef long long ll;
using namespace std;

ll bs(int a, int b){
    ll lo = 1, hi = 1e16;
    ll ans = -1;
    while(lo <= hi){
        ll mid = (lo+hi)/2;
        ll c = floor((double)mid*0.08L);
        ll c2 = floor((double)mid*0.1L);
        if( c == a && c2 == b){
            ans = mid;
            hi = mid-1;
        }
        else if( c > a )
            hi = mid-1;
        else
            lo = mid+1;
    }
    return ans;
}


int main(){
    int a , b;
    cin >> a >> b;
    cout << bs(a, b) << endl;
}