import java.util.*;
 
public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
		int n8 = sc.nextInt();
        int n10 = sc.nextInt();
        for(int i = 1; i <= 1000; i++){
        	if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	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 n8 = sc.nextInt();
        int n10 = sc.nextInt();
        for(int i = 1; i <= 1000; i++){
        	if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	System.out.println(i);
                return;
            }
        }
        System.out.println("-1");
    }
} Main public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
		int n8 = sc.nextInt();
        int n10 = sc.nextInt();
        for(int i = 1; i <= 1000; i++){
        	if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	System.out.println(i);
                return;
            }
        }
        System.out.println("-1");
    } main {
    	Scanner sc = new Scanner(System.in);
		int n8 = sc.nextInt();
        int n10 = sc.nextInt();
        for(int i = 1; i <= 1000; i++){
        	if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	System.out.println(i);
                return;
            }
        }
        System.out.println("-1");
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n8 = sc.nextInt(); n8 sc.nextInt() sc.nextInt sc int n10 = sc.nextInt(); n10 sc.nextInt() sc.nextInt sc for(int i = 1; i <= 1000; i++){
        	if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	System.out.println(i);
                return;
            }
        } int i = 1; int i = 1; i 1 i <= 1000 i 1000 i++ i++ i {
        	if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	System.out.println(i);
                return;
            }
        } {
        	if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	System.out.println(i);
                return;
            }
        } if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	System.out.println(i);
                return;
            } (int)(i * 0.08) == n8 && (int)(i * 0.1) == n10 (int)(i * 0.08) == n8 (int)(i * 0.08) i 0.08 n8 (int)(i * 0.1) == n10 (int)(i * 0.1) i 0.1 n10 {
            	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 sc = new Scanner(System.in);
		int n8 = sc.nextInt();
        int n10 = sc.nextInt();
        for(int i = 1; i <= 1000; i++){
        	if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	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 n8 = sc.nextInt();
        int n10 = sc.nextInt();
        for(int i = 1; i <= 1000; i++){
        	if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	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 n8 = sc.nextInt();
        int n10 = sc.nextInt();
        for(int i = 1; i <= 1000; i++){
        	if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	System.out.println(i);
                return;
            }
        }
        System.out.println("-1");
    }
} 