import 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();
    for(int i = 0;i <= 1250;i++){
      if(A == Math.floor(i*0.08) && B == Math.floor(i*0.1)){
        System.out.print(i);
        break;
      }else if(i == 1250){
        System.out.print(-1);
      }
    }
  }
} import java.util.*; util.* java public 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 = 0;i <= 1250;i++){
      if(A == Math.floor(i*0.08) && B == Math.floor(i*0.1)){
        System.out.print(i);
        break;
      }else if(i == 1250){
        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();
    for(int i = 0;i <= 1250;i++){
      if(A == Math.floor(i*0.08) && B == Math.floor(i*0.1)){
        System.out.print(i);
        break;
      }else if(i == 1250){
        System.out.print(-1);
      }
    }
  } main {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    for(int i = 0;i <= 1250;i++){
      if(A == Math.floor(i*0.08) && B == Math.floor(i*0.1)){
        System.out.print(i);
        break;
      }else if(i == 1250){
        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 for(int i = 0;i <= 1250;i++){
      if(A == Math.floor(i*0.08) && B == Math.floor(i*0.1)){
        System.out.print(i);
        break;
      }else if(i == 1250){
        System.out.print(-1);
      }
    } int i = 0; int i = 0; i 0 i <= 1250 i 1250 i++ i++ i {
      if(A == Math.floor(i*0.08) && B == Math.floor(i*0.1)){
        System.out.print(i);
        break;
      }else if(i == 1250){
        System.out.print(-1);
      }
    } {
      if(A == Math.floor(i*0.08) && B == Math.floor(i*0.1)){
        System.out.print(i);
        break;
      }else if(i == 1250){
        System.out.print(-1);
      }
    } if(A == Math.floor(i*0.08) && B == Math.floor(i*0.1)){
        System.out.print(i);
        break;
      }else if(i == 1250){
        System.out.print(-1);
      } A == Math.floor(i*0.08) && B == Math.floor(i*0.1) A == Math.floor(i*0.08) A Math.floor(i*0.08) Math.floor Math i*0.08 i 0.08 B == Math.floor(i*0.1) B Math.floor(i*0.1) Math.floor Math i*0.1 i 0.1 {
        System.out.print(i);
        break;
      } System.out.print(i) System.out.print System.out System System.out i break; if(i == 1250){
        System.out.print(-1);
      } i == 1250 i 1250 {
        System.out.print(-1);
      } System.out.print(-1) System.out.print System.out System System.out -1 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();
    for(int i = 0;i <= 1250;i++){
      if(A == Math.floor(i*0.08) && B == Math.floor(i*0.1)){
        System.out.print(i);
        break;
      }else if(i == 1250){
        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();
    for(int i = 0;i <= 1250;i++){
      if(A == Math.floor(i*0.08) && B == Math.floor(i*0.1)){
        System.out.print(i);
        break;
      }else if(i == 1250){
        System.out.print(-1);
      }
    }
  }
} Main
import 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();
    for(int i = 0;i <= 1250;i++){
      if(A == Math.floor(i*0.08) && B == Math.floor(i*0.1)){
        System.out.print(i);
        break;
      }else if(i == 1250){
        System.out.print(-1);
      }
    }
  }
}