import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		
		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		for(int i = 10; i < 1010; i++) {
			if((int)(i * 0.08) == a && (int)(i*0.1) == 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 stdIn = new Scanner(System.in);
		
		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		for(int i = 10; i < 1010; i++) {
			if((int)(i * 0.08) == a && (int)(i*0.1) == b) {
				System.out.println(i);
				return;
			}
		}
		System.out.println("-1");
		
	}

} Main public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		
		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		for(int i = 10; i < 1010; i++) {
			if((int)(i * 0.08) == a && (int)(i*0.1) == b) {
				System.out.println(i);
				return;
			}
		}
		System.out.println("-1");
		
	} main {
		Scanner stdIn = new Scanner(System.in);
		
		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		for(int i = 10; i < 1010; i++) {
			if((int)(i * 0.08) == a && (int)(i*0.1) == b) {
				System.out.println(i);
				return;
			}
		}
		System.out.println("-1");
		
	} Scanner stdIn = new Scanner(System.in); stdIn new Scanner(System.in) int a = stdIn.nextInt(); a stdIn.nextInt() stdIn.nextInt stdIn int b = stdIn.nextInt(); b stdIn.nextInt() stdIn.nextInt stdIn for(int i = 10; i < 1010; i++) {
			if((int)(i * 0.08) == a && (int)(i*0.1) == b) {
				System.out.println(i);
				return;
			}
		} int i = 10; int i = 10; i 10 i < 1010 i 1010 i++ i++ i {
			if((int)(i * 0.08) == a && (int)(i*0.1) == b) {
				System.out.println(i);
				return;
			}
		} {
			if((int)(i * 0.08) == a && (int)(i*0.1) == b) {
				System.out.println(i);
				return;
			}
		} if((int)(i * 0.08) == a && (int)(i*0.1) == b) {
				System.out.println(i);
				return;
			} (int)(i * 0.08) == a && (int)(i*0.1) == b (int)(i * 0.08) == a (int)(i * 0.08) i 0.08 a (int)(i*0.1) == b (int)(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" String[] args args public class Main {

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		
		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		for(int i = 10; i < 1010; i++) {
			if((int)(i * 0.08) == a && (int)(i*0.1) == b) {
				System.out.println(i);
				return;
			}
		}
		System.out.println("-1");
		
	}

} public class Main {

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		
		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		for(int i = 10; i < 1010; i++) {
			if((int)(i * 0.08) == a && (int)(i*0.1) == 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 stdIn = new Scanner(System.in);
		
		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		for(int i = 10; i < 1010; i++) {
			if((int)(i * 0.08) == a && (int)(i*0.1) == b) {
				System.out.println(i);
				return;
			}
		}
		System.out.println("-1");
		
	}

}
