import java.util.Scanner;

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 < 2000; i++) {
            int tmp1 = (int) (i * 0.08);
            int tmp2 = (int) (i * 0.1);
            if(tmp1 == a && tmp2 == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
} import java.util.Scanner; Scanner 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 < 2000; i++) {
            int tmp1 = (int) (i * 0.08);
            int tmp2 = (int) (i * 0.1);
            if(tmp1 == a && tmp2 == 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 < 2000; i++) {
            int tmp1 = (int) (i * 0.08);
            int tmp2 = (int) (i * 0.1);
            if(tmp1 == a && tmp2 == 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 < 2000; i++) {
            int tmp1 = (int) (i * 0.08);
            int tmp2 = (int) (i * 0.1);
            if(tmp1 == a && tmp2 == 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 < 2000; i++) {
            int tmp1 = (int) (i * 0.08);
            int tmp2 = (int) (i * 0.1);
            if(tmp1 == a && tmp2 == b) {
                System.out.println(i);
                return;
            }
        } int i = 1; int i = 1; i 1 i < 2000 i 2000 i++ i++ i {
            int tmp1 = (int) (i * 0.08);
            int tmp2 = (int) (i * 0.1);
            if(tmp1 == a && tmp2 == b) {
                System.out.println(i);
                return;
            }
        } {
            int tmp1 = (int) (i * 0.08);
            int tmp2 = (int) (i * 0.1);
            if(tmp1 == a && tmp2 == b) {
                System.out.println(i);
                return;
            }
        } int tmp1 = (int) (i * 0.08); tmp1 (int) (i * 0.08) i 0.08 int tmp2 = (int) (i * 0.1); tmp2 (int) (i * 0.1) i 0.1 if(tmp1 == a && tmp2 == b) {
                System.out.println(i);
                return;
            } tmp1 == a && tmp2 == b tmp1 == a tmp1 a tmp2 == b tmp2 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 < 2000; i++) {
            int tmp1 = (int) (i * 0.08);
            int tmp2 = (int) (i * 0.1);
            if(tmp1 == a && tmp2 == 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 < 2000; i++) {
            int tmp1 = (int) (i * 0.08);
            int tmp2 = (int) (i * 0.1);
            if(tmp1 == a && tmp2 == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
} Main
import java.util.Scanner;

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 < 2000; i++) {
            int tmp1 = (int) (i * 0.08);
            int tmp2 = (int) (i * 0.1);
            if(tmp1 == a && tmp2 == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
}
