import java.util.*;

class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
      
    for(int i=1;i<10001;i++){
      if(Math.floor(i*0.1)==b){
        if(Math.floor(i*0.08)==a){
          System.out.println(i);
          return;
        }
      }
    }
    System.out.println(-1);
  }
} import java.util.*; util.* java class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
      
    for(int i=1;i<10001;i++){
      if(Math.floor(i*0.1)==b){
        if(Math.floor(i*0.08)==a){
          System.out.println(i);
          return;
        }
      }
    }
    System.out.println(-1);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
      
    for(int i=1;i<10001;i++){
      if(Math.floor(i*0.1)==b){
        if(Math.floor(i*0.08)==a){
          System.out.println(i);
          return;
        }
      }
    }
    System.out.println(-1);
  } main {
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
      
    for(int i=1;i<10001;i++){
      if(Math.floor(i*0.1)==b){
        if(Math.floor(i*0.08)==a){
          System.out.println(i);
          return;
        }
      }
    }
    System.out.println(-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 for(int i=1;i<10001;i++){
      if(Math.floor(i*0.1)==b){
        if(Math.floor(i*0.08)==a){
          System.out.println(i);
          return;
        }
      }
    } int i=1; int i=1; i 1 i<10001 i 10001 i++ i++ i {
      if(Math.floor(i*0.1)==b){
        if(Math.floor(i*0.08)==a){
          System.out.println(i);
          return;
        }
      }
    } {
      if(Math.floor(i*0.1)==b){
        if(Math.floor(i*0.08)==a){
          System.out.println(i);
          return;
        }
      }
    } if(Math.floor(i*0.1)==b){
        if(Math.floor(i*0.08)==a){
          System.out.println(i);
          return;
        }
      } Math.floor(i*0.1)==b Math.floor(i*0.1) Math.floor Math i*0.1 i 0.1 b {
        if(Math.floor(i*0.08)==a){
          System.out.println(i);
          return;
        }
      } if(Math.floor(i*0.08)==a){
          System.out.println(i);
          return;
        } Math.floor(i*0.08)==a Math.floor(i*0.08) Math.floor Math i*0.08 i 0.08 a {
          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 1 String[] args args
import java.util.*;

class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
      
    for(int i=1;i<10001;i++){
      if(Math.floor(i*0.1)==b){
        if(Math.floor(i*0.08)==a){
          System.out.println(i);
          return;
        }
      }
    }
    System.out.println(-1);
  }
}