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 = 1; i<10000000; i++){
            int val1 = (int) (0.08 * i);
            int val2 = (int) (0.1 * i);
            if(val1 == a && val2 == b){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-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 = 1; i<10000000; i++){
            int val1 = (int) (0.08 * i);
            int val2 = (int) (0.1 * i);
            if(val1 == a && val2 == b){
                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<10000000; i++){
            int val1 = (int) (0.08 * i);
            int val2 = (int) (0.1 * i);
            if(val1 == a && val2 == b){
                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<10000000; i++){
            int val1 = (int) (0.08 * i);
            int val2 = (int) (0.1 * i);
            if(val1 == a && val2 == b){
                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<10000000; i++){
            int val1 = (int) (0.08 * i);
            int val2 = (int) (0.1 * i);
            if(val1 == a && val2 == b){
                System.out.println(i);
                return;
            }
        } int i = 1; int i = 1; i 1 i<10000000 i 10000000 i++ i++ i {
            int val1 = (int) (0.08 * i);
            int val2 = (int) (0.1 * i);
            if(val1 == a && val2 == b){
                System.out.println(i);
                return;
            }
        } {
            int val1 = (int) (0.08 * i);
            int val2 = (int) (0.1 * i);
            if(val1 == a && val2 == b){
                System.out.println(i);
                return;
            }
        } int val1 = (int) (0.08 * i); val1 (int) (0.08 * i) 0.08 i int val2 = (int) (0.1 * i); val2 (int) (0.1 * i) 0.1 i if(val1 == a && val2 == b){
                System.out.println(i);
                return;
            } val1 == a && val2 == b val1 == a val1 a val2 == b val2 b {
                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 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 = 1; i<10000000; i++){
            int val1 = (int) (0.08 * i);
            int val2 = (int) (0.1 * i);
            if(val1 == a && val2 == b){
                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 a = sc.nextInt();
        int b = sc.nextInt();
        for(int i = 1; i<10000000; i++){
            int val1 = (int) (0.08 * i);
            int val2 = (int) (0.1 * i);
            if(val1 == a && val2 == b){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-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 = 1; i<10000000; i++){
            int val1 = (int) (0.08 * i);
            int val2 = (int) (0.1 * i);
            if(val1 == a && val2 == b){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
}