import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		        Scanner sc = new Scanner(System.in);


		       int hati = sc.nextInt();
		       int juu = sc.nextInt();

		       for(int i = 1; i <= 1000;i++) {
		    	   if((int)(i*0.08) ==hati && (int)(i*0.1) ==juu) {
		    		   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 hati = sc.nextInt();
		       int juu = sc.nextInt();

		       for(int i = 1; i <= 1000;i++) {
		    	   if((int)(i*0.08) ==hati && (int)(i*0.1) ==juu) {
		    		   System.out.println(i);
		    		   return;
		    	   }
		       }
		       System.out.println("-1");



	}
		} Main public static void main(String[] args) {
		        Scanner sc = new Scanner(System.in);


		       int hati = sc.nextInt();
		       int juu = sc.nextInt();

		       for(int i = 1; i <= 1000;i++) {
		    	   if((int)(i*0.08) ==hati && (int)(i*0.1) ==juu) {
		    		   System.out.println(i);
		    		   return;
		    	   }
		       }
		       System.out.println("-1");



	} main {
		        Scanner sc = new Scanner(System.in);


		       int hati = sc.nextInt();
		       int juu = sc.nextInt();

		       for(int i = 1; i <= 1000;i++) {
		    	   if((int)(i*0.08) ==hati && (int)(i*0.1) ==juu) {
		    		   System.out.println(i);
		    		   return;
		    	   }
		       }
		       System.out.println("-1");



	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int hati = sc.nextInt(); hati sc.nextInt() sc.nextInt sc int juu = sc.nextInt(); juu sc.nextInt() sc.nextInt sc for(int i = 1; i <= 1000;i++) {
		    	   if((int)(i*0.08) ==hati && (int)(i*0.1) ==juu) {
		    		   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) ==hati && (int)(i*0.1) ==juu) {
		    		   System.out.println(i);
		    		   return;
		    	   }
		       } {
		    	   if((int)(i*0.08) ==hati && (int)(i*0.1) ==juu) {
		    		   System.out.println(i);
		    		   return;
		    	   }
		       } if((int)(i*0.08) ==hati && (int)(i*0.1) ==juu) {
		    		   System.out.println(i);
		    		   return;
		    	   } (int)(i*0.08) ==hati && (int)(i*0.1) ==juu (int)(i*0.08) ==hati (int)(i*0.08) i 0.08 hati (int)(i*0.1) ==juu (int)(i*0.1) i 0.1 juu {
		    		   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 hati = sc.nextInt();
		       int juu = sc.nextInt();

		       for(int i = 1; i <= 1000;i++) {
		    	   if((int)(i*0.08) ==hati && (int)(i*0.1) ==juu) {
		    		   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 hati = sc.nextInt();
		       int juu = sc.nextInt();

		       for(int i = 1; i <= 1000;i++) {
		    	   if((int)(i*0.08) ==hati && (int)(i*0.1) ==juu) {
		    		   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 hati = sc.nextInt();
		       int juu = sc.nextInt();

		       for(int i = 1; i <= 1000;i++) {
		    	   if((int)(i*0.08) ==hati && (int)(i*0.1) ==juu) {
		    		   System.out.println(i);
		    		   return;
		    	   }
		       }
		       System.out.println("-1");



	}
		}

