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 < 10000; i++) {
            if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == 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 = 0; i < 10000; i++) {
            if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == 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 = 0; i < 10000; i++) {
            if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == 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 = 0; i < 10000; i++) {
            if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == 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 = 0; i < 10000; i++) {
            if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
                System.out.println(i);
                return;
            }
        } int i = 0; int i = 0; i 0 i < 10000 i 10000 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.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 = 0; i < 10000; i++) {
            if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == 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 = 0; i < 10000; i++) {
            if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == 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 = 0; i < 10000; i++) {
            if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
                System.out.println(i);
                return;
            }
        }

        System.out.println(-1);
    }
}
