import java.io.BufferedInputStream;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc=new Scanner(new BufferedInputStream(System.in));
        int a=sc.nextInt();
        int b=sc.nextInt();
        int flag=0;
        for(int i=b*10;i<=b*10+9;i++)
            if((int)(i*0.08)==a) {
                System.out.println(i);
                flag++;
                break;
            }
        if(flag==0)
            System.out.println("-1");

    }
} import java.io.BufferedInputStream; BufferedInputStream java.io import java.math.BigInteger; BigInteger java.math import java.util.Arrays; Arrays java.util import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc=new Scanner(new BufferedInputStream(System.in));
        int a=sc.nextInt();
        int b=sc.nextInt();
        int flag=0;
        for(int i=b*10;i<=b*10+9;i++)
            if((int)(i*0.08)==a) {
                System.out.println(i);
                flag++;
                break;
            }
        if(flag==0)
            System.out.println("-1");

    }
} Main public static void main(String[] args) {
        Scanner sc=new Scanner(new BufferedInputStream(System.in));
        int a=sc.nextInt();
        int b=sc.nextInt();
        int flag=0;
        for(int i=b*10;i<=b*10+9;i++)
            if((int)(i*0.08)==a) {
                System.out.println(i);
                flag++;
                break;
            }
        if(flag==0)
            System.out.println("-1");

    } main {
        Scanner sc=new Scanner(new BufferedInputStream(System.in));
        int a=sc.nextInt();
        int b=sc.nextInt();
        int flag=0;
        for(int i=b*10;i<=b*10+9;i++)
            if((int)(i*0.08)==a) {
                System.out.println(i);
                flag++;
                break;
            }
        if(flag==0)
            System.out.println("-1");

    } Scanner sc=new Scanner(new BufferedInputStream(System.in)); sc new Scanner(new BufferedInputStream(System.in)) int a=sc.nextInt(); a sc.nextInt() sc.nextInt sc int b=sc.nextInt(); b sc.nextInt() sc.nextInt sc int flag=0; flag 0 for(int i=b*10;i<=b*10+9;i++)
            if((int)(i*0.08)==a) {
                System.out.println(i);
                flag++;
                break;
            } int i=b*10; int i=b*10; i b*10 b 10 i<=b*10+9 i b*10+9 b*10 b 10 9 i++ i++ i if((int)(i*0.08)==a) {
                System.out.println(i);
                flag++;
                break;
            } if((int)(i*0.08)==a) {
                System.out.println(i);
                flag++;
                break;
            } (int)(i*0.08)==a (int)(i*0.08) i 0.08 a {
                System.out.println(i);
                flag++;
                break;
            } System.out.println(i) System.out.println System.out System System.out i flag++ flag break; if(flag==0)
            System.out.println("-1"); flag==0 flag 0 System.out.println("-1") System.out.println System.out System System.out "-1" String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc=new Scanner(new BufferedInputStream(System.in));
        int a=sc.nextInt();
        int b=sc.nextInt();
        int flag=0;
        for(int i=b*10;i<=b*10+9;i++)
            if((int)(i*0.08)==a) {
                System.out.println(i);
                flag++;
                break;
            }
        if(flag==0)
            System.out.println("-1");

    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc=new Scanner(new BufferedInputStream(System.in));
        int a=sc.nextInt();
        int b=sc.nextInt();
        int flag=0;
        for(int i=b*10;i<=b*10+9;i++)
            if((int)(i*0.08)==a) {
                System.out.println(i);
                flag++;
                break;
            }
        if(flag==0)
            System.out.println("-1");

    }
} Main
import java.io.BufferedInputStream;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc=new Scanner(new BufferedInputStream(System.in));
        int a=sc.nextInt();
        int b=sc.nextInt();
        int flag=0;
        for(int i=b*10;i<=b*10+9;i++)
            if((int)(i*0.08)==a) {
                System.out.println(i);
                flag++;
                break;
            }
        if(flag==0)
            System.out.println("-1");

    }
}