import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);
      int A = sc.nextInt();
      int B = sc.nextInt();
      int i;
      for(i=1;i<=1000;i++){
        if(Math.floor(i*0.08)==A && Math.floor(i*0.1)==B){
          System.out.println(i);
          return;
        }
      }
        System.out.print("-1");
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);
      int A = sc.nextInt();
      int B = sc.nextInt();
      int i;
      for(i=1;i<=1000;i++){
        if(Math.floor(i*0.08)==A && Math.floor(i*0.1)==B){
          System.out.println(i);
          return;
        }
      }
        System.out.print("-1");
    }
} Main public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);
      int A = sc.nextInt();
      int B = sc.nextInt();
      int i;
      for(i=1;i<=1000;i++){
        if(Math.floor(i*0.08)==A && Math.floor(i*0.1)==B){
          System.out.println(i);
          return;
        }
      }
        System.out.print("-1");
    } main {
      Scanner sc = new Scanner(System.in);
      int A = sc.nextInt();
      int B = sc.nextInt();
      int i;
      for(i=1;i<=1000;i++){
        if(Math.floor(i*0.08)==A && Math.floor(i*0.1)==B){
          System.out.println(i);
          return;
        }
      }
        System.out.print("-1");
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int A = sc.nextInt(); A sc.nextInt() sc.nextInt sc int B = sc.nextInt(); B sc.nextInt() sc.nextInt sc int i; i for(i=1;i<=1000;i++){
        if(Math.floor(i*0.08)==A && Math.floor(i*0.1)==B){
          System.out.println(i);
          return;
        }
      } i=1; i=1 i 1 i<=1000 i 1000 i++ i++ i {
        if(Math.floor(i*0.08)==A && Math.floor(i*0.1)==B){
          System.out.println(i);
          return;
        }
      } {
        if(Math.floor(i*0.08)==A && Math.floor(i*0.1)==B){
          System.out.println(i);
          return;
        }
      } if(Math.floor(i*0.08)==A && Math.floor(i*0.1)==B){
          System.out.println(i);
          return;
        } Math.floor(i*0.08)==A && Math.floor(i*0.1)==B Math.floor(i*0.08)==A Math.floor(i*0.08) Math.floor Math i*0.08 i 0.08 A Math.floor(i*0.1)==B Math.floor(i*0.1) Math.floor Math i*0.1 i 0.1 B {
          System.out.println(i);
          return;
        } System.out.println(i) System.out.println System.out System System.out i return; System.out.print("-1") System.out.print 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 A = sc.nextInt();
      int B = sc.nextInt();
      int i;
      for(i=1;i<=1000;i++){
        if(Math.floor(i*0.08)==A && Math.floor(i*0.1)==B){
          System.out.println(i);
          return;
        }
      }
        System.out.print("-1");
    }
} public class Main {
    public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);
      int A = sc.nextInt();
      int B = sc.nextInt();
      int i;
      for(i=1;i<=1000;i++){
        if(Math.floor(i*0.08)==A && Math.floor(i*0.1)==B){
          System.out.println(i);
          return;
        }
      }
        System.out.print("-1");
    }
} Main
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);
      int A = sc.nextInt();
      int B = sc.nextInt();
      int i;
      for(i=1;i<=1000;i++){
        if(Math.floor(i*0.08)==A && Math.floor(i*0.1)==B){
          System.out.println(i);
          return;
        }
      }
        System.out.print("-1");
    }
}
