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 <= 10000; i++) {
			int num1 =(int) (i*0.08);
			int num2 = (int) (i*0.10);
			if(num1 == a && num2 == 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 <= 10000; i++) {
			int num1 =(int) (i*0.08);
			int num2 = (int) (i*0.10);
			if(num1 == a && num2 == 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 <= 10000; i++) {
			int num1 =(int) (i*0.08);
			int num2 = (int) (i*0.10);
			if(num1 == a && num2 == 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 <= 10000; i++) {
			int num1 =(int) (i*0.08);
			int num2 = (int) (i*0.10);
			if(num1 == a && num2 == 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 <= 10000; i++) {
			int num1 =(int) (i*0.08);
			int num2 = (int) (i*0.10);
			if(num1 == a && num2 == b) {
				System.out.println(i);
				return;
			}
		} int i = 1; int i = 1; i 1 i <= 10000 i 10000 i++ i++ i {
			int num1 =(int) (i*0.08);
			int num2 = (int) (i*0.10);
			if(num1 == a && num2 == b) {
				System.out.println(i);
				return;
			}
		} {
			int num1 =(int) (i*0.08);
			int num2 = (int) (i*0.10);
			if(num1 == a && num2 == b) {
				System.out.println(i);
				return;
			}
		} int num1 =(int) (i*0.08); num1 (int) (i*0.08) i 0.08 int num2 = (int) (i*0.10); num2 (int) (i*0.10) i 0.10 if(num1 == a && num2 == b) {
				System.out.println(i);
				return;
			} num1 == a && num2 == b num1 == a num1 a num2 == b num2 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 <= 10000; i++) {
			int num1 =(int) (i*0.08);
			int num2 = (int) (i*0.10);
			if(num1 == a && num2 == 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 <= 10000; i++) {
			int num1 =(int) (i*0.08);
			int num2 = (int) (i*0.10);
			if(num1 == a && num2 == 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 <= 10000; i++) {
			int num1 =(int) (i*0.08);
			int num2 = (int) (i*0.10);
			if(num1 == a && num2 == b) {
				System.out.println(i);
				return;
			}
		}
		System.out.println(-1);
	}
}
