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<10001; i++) {
            int aa = (int) (i * 0.08);
            int bb = (int) (i * 0.1);
            if(a == aa && b == bb) {
                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<10001; i++) {
            int aa = (int) (i * 0.08);
            int bb = (int) (i * 0.1);
            if(a == aa && b == bb) {
                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<10001; i++) {
            int aa = (int) (i * 0.08);
            int bb = (int) (i * 0.1);
            if(a == aa && b == bb) {
                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<10001; i++) {
            int aa = (int) (i * 0.08);
            int bb = (int) (i * 0.1);
            if(a == aa && b == bb) {
                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<10001; i++) {
            int aa = (int) (i * 0.08);
            int bb = (int) (i * 0.1);
            if(a == aa && b == bb) {
                System.out.println(i);
                return;
            }
        } int i=1; int i=1; i 1 i<10001 i 10001 i++ i++ i {
            int aa = (int) (i * 0.08);
            int bb = (int) (i * 0.1);
            if(a == aa && b == bb) {
                System.out.println(i);
                return;
            }
        } {
            int aa = (int) (i * 0.08);
            int bb = (int) (i * 0.1);
            if(a == aa && b == bb) {
                System.out.println(i);
                return;
            }
        } int aa = (int) (i * 0.08); aa (int) (i * 0.08) i 0.08 int bb = (int) (i * 0.1); bb (int) (i * 0.1) i 0.1 if(a == aa && b == bb) {
                System.out.println(i);
                return;
            } a == aa && b == bb a == aa a aa b == bb b bb {
                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<10001; i++) {
            int aa = (int) (i * 0.08);
            int bb = (int) (i * 0.1);
            if(a == aa && b == bb) {
                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<10001; i++) {
            int aa = (int) (i * 0.08);
            int bb = (int) (i * 0.1);
            if(a == aa && b == bb) {
                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<10001; i++) {
            int aa = (int) (i * 0.08);
            int bb = (int) (i * 0.1);
            if(a == aa && b == bb) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
}