    import java.util.Scanner;
    public class Main{
    	public static void main(String[] args) {
    		Scanner sc = new Scanner(System.in);
    		 int x =sc.nextInt();
    		 int y =sc.nextInt();
    		 
    		 for(int i=1; i<=100000; i++) {
    		 if((int)(i*0.08)==x && (int)(i*0.1)==y) {
    			 System.out.println(i);
    			 return;
    		 	}
    		 }	
    			 System.out.println("-1");
        }
    } import java.util.Scanner; Scanner java.util public class Main{
    	public static void main(String[] args) {
    		Scanner sc = new Scanner(System.in);
    		 int x =sc.nextInt();
    		 int y =sc.nextInt();
    		 
    		 for(int i=1; i<=100000; i++) {
    		 if((int)(i*0.08)==x && (int)(i*0.1)==y) {
    			 System.out.println(i);
    			 return;
    		 	}
    		 }	
    			 System.out.println("-1");
        }
    } Main public static void main(String[] args) {
    		Scanner sc = new Scanner(System.in);
    		 int x =sc.nextInt();
    		 int y =sc.nextInt();
    		 
    		 for(int i=1; i<=100000; i++) {
    		 if((int)(i*0.08)==x && (int)(i*0.1)==y) {
    			 System.out.println(i);
    			 return;
    		 	}
    		 }	
    			 System.out.println("-1");
        } main {
    		Scanner sc = new Scanner(System.in);
    		 int x =sc.nextInt();
    		 int y =sc.nextInt();
    		 
    		 for(int i=1; i<=100000; i++) {
    		 if((int)(i*0.08)==x && (int)(i*0.1)==y) {
    			 System.out.println(i);
    			 return;
    		 	}
    		 }	
    			 System.out.println("-1");
        } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int x =sc.nextInt(); x sc.nextInt() sc.nextInt sc int y =sc.nextInt(); y sc.nextInt() sc.nextInt sc for(int i=1; i<=100000; i++) {
    		 if((int)(i*0.08)==x && (int)(i*0.1)==y) {
    			 System.out.println(i);
    			 return;
    		 	}
    		 } int i=1; int i=1; i 1 i<=100000 i 100000 i++ i++ i {
    		 if((int)(i*0.08)==x && (int)(i*0.1)==y) {
    			 System.out.println(i);
    			 return;
    		 	}
    		 } {
    		 if((int)(i*0.08)==x && (int)(i*0.1)==y) {
    			 System.out.println(i);
    			 return;
    		 	}
    		 } if((int)(i*0.08)==x && (int)(i*0.1)==y) {
    			 System.out.println(i);
    			 return;
    		 	} (int)(i*0.08)==x && (int)(i*0.1)==y (int)(i*0.08)==x (int)(i*0.08) i 0.08 x (int)(i*0.1)==y (int)(i*0.1) i 0.1 y {
    			 System.out.println(i);
    			 return;
    		 	} System.out.println(i) System.out.println System.out System System.out i return; 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(System.in);
    		 int x =sc.nextInt();
    		 int y =sc.nextInt();
    		 
    		 for(int i=1; i<=100000; i++) {
    		 if((int)(i*0.08)==x && (int)(i*0.1)==y) {
    			 System.out.println(i);
    			 return;
    		 	}
    		 }	
    			 System.out.println("-1");
        }
    } public class Main{
    	public static void main(String[] args) {
    		Scanner sc = new Scanner(System.in);
    		 int x =sc.nextInt();
    		 int y =sc.nextInt();
    		 
    		 for(int i=1; i<=100000; i++) {
    		 if((int)(i*0.08)==x && (int)(i*0.1)==y) {
    			 System.out.println(i);
    			 return;
    		 	}
    		 }	
    			 System.out.println("-1");
        }
    } Main
    import java.util.Scanner;
    public class Main{
    	public static void main(String[] args) {
    		Scanner sc = new Scanner(System.in);
    		 int x =sc.nextInt();
    		 int y =sc.nextInt();
    		 
    		 for(int i=1; i<=100000; i++) {
    		 if((int)(i*0.08)==x && (int)(i*0.1)==y) {
    			 System.out.println(i);
    			 return;
    		 	}
    		 }	
    			 System.out.println("-1");
        }
    }