
import java.util.Scanner;

/**
 * 增税
 */
public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {
        int a = sc.nextInt();
        int b = sc.nextInt();

        int ans = -1;
        for (int i =0; i< 10009; i++){
            if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            }
        }

        System.out.println(ans);

    }
} import java.util.Scanner; Scanner java.util public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {
        int a = sc.nextInt();
        int b = sc.nextInt();

        int ans = -1;
        for (int i =0; i< 10009; i++){
            if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            }
        }

        System.out.println(ans);

    }
} Main static Scanner sc = new Scanner(System.in); sc new Scanner(System.in) public static void main(String[] args) {
        int a = sc.nextInt();
        int b = sc.nextInt();

        int ans = -1;
        for (int i =0; i< 10009; i++){
            if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            }
        }

        System.out.println(ans);

    } main {
        int a = sc.nextInt();
        int b = sc.nextInt();

        int ans = -1;
        for (int i =0; i< 10009; i++){
            if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            }
        }

        System.out.println(ans);

    } int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc int ans = -1; ans -1 1 for (int i =0; i< 10009; i++){
            if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            }
        } int i =0; int i =0; i 0 i< 10009 i 10009 i++ i++ i {
            if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            }
        } {
            if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            }
        } if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            } (int) (i * 0.08) == a (int) (i * 0.08) i 0.08 a {
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            } if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                } (int) (i * 0.1) == b (int) (i * 0.1) i 0.1 b {
                    ans = i;
                    break;
                } ans = i ans i break; System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {
        int a = sc.nextInt();
        int b = sc.nextInt();

        int ans = -1;
        for (int i =0; i< 10009; i++){
            if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            }
        }

        System.out.println(ans);

    }
} public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {
        int a = sc.nextInt();
        int b = sc.nextInt();

        int ans = -1;
        for (int i =0; i< 10009; i++){
            if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            }
        }

        System.out.println(ans);

    }
} Main

import java.util.Scanner;

/**
 * 增税
 */
public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {
        int a = sc.nextInt();
        int b = sc.nextInt();

        int ans = -1;
        for (int i =0; i< 10009; i++){
            if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == b ){
                    ans = i;
                    break;
                }
            }
        }

        System.out.println(ans);

    }
}
