import java.util.*;

public class Main {
	public static void main(String[] args) throws Exception{
		Scanner scn = new Scanner(System.in);
		int a = scn.nextInt();
      	int b = scn.nextInt();
      	int ans = -1;
      	for(int i=1; i<=1000; i++){
          if((int)(i*0.08)==a && (int)(i*0.1)==b){
            ans = i;
            break;
          }
        }
		System.out.println(ans);
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args) throws Exception{
		Scanner scn = new Scanner(System.in);
		int a = scn.nextInt();
      	int b = scn.nextInt();
      	int ans = -1;
      	for(int i=1; i<=1000; i++){
          if((int)(i*0.08)==a && (int)(i*0.1)==b){
            ans = i;
            break;
          }
        }
		System.out.println(ans);
	}
} Main public static void main(String[] args) throws Exception{
		Scanner scn = new Scanner(System.in);
		int a = scn.nextInt();
      	int b = scn.nextInt();
      	int ans = -1;
      	for(int i=1; i<=1000; i++){
          if((int)(i*0.08)==a && (int)(i*0.1)==b){
            ans = i;
            break;
          }
        }
		System.out.println(ans);
	} main {
		Scanner scn = new Scanner(System.in);
		int a = scn.nextInt();
      	int b = scn.nextInt();
      	int ans = -1;
      	for(int i=1; i<=1000; i++){
          if((int)(i*0.08)==a && (int)(i*0.1)==b){
            ans = i;
            break;
          }
        }
		System.out.println(ans);
	} Scanner scn = new Scanner(System.in); scn new Scanner(System.in) int a = scn.nextInt(); a scn.nextInt() scn.nextInt scn int b = scn.nextInt(); b scn.nextInt() scn.nextInt scn int ans = -1; ans -1 1 for(int i=1; i<=1000; i++){
          if((int)(i*0.08)==a && (int)(i*0.1)==b){
            ans = i;
            break;
          }
        } int i=1; int i=1; i 1 i<=1000 i 1000 i++ i++ i {
          if((int)(i*0.08)==a && (int)(i*0.1)==b){
            ans = i;
            break;
          }
        } {
          if((int)(i*0.08)==a && (int)(i*0.1)==b){
            ans = i;
            break;
          }
        } if((int)(i*0.08)==a && (int)(i*0.1)==b){
            ans = i;
            break;
          } (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 {
            ans = i;
            break;
          } ans = i ans i break; System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
	public static void main(String[] args) throws Exception{
		Scanner scn = new Scanner(System.in);
		int a = scn.nextInt();
      	int b = scn.nextInt();
      	int ans = -1;
      	for(int i=1; i<=1000; i++){
          if((int)(i*0.08)==a && (int)(i*0.1)==b){
            ans = i;
            break;
          }
        }
		System.out.println(ans);
	}
} public class Main {
	public static void main(String[] args) throws Exception{
		Scanner scn = new Scanner(System.in);
		int a = scn.nextInt();
      	int b = scn.nextInt();
      	int ans = -1;
      	for(int i=1; i<=1000; i++){
          if((int)(i*0.08)==a && (int)(i*0.1)==b){
            ans = i;
            break;
          }
        }
		System.out.println(ans);
	}
} Main
import java.util.*;

public class Main {
	public static void main(String[] args) throws Exception{
		Scanner scn = new Scanner(System.in);
		int a = scn.nextInt();
      	int b = scn.nextInt();
      	int ans = -1;
      	for(int i=1; i<=1000; i++){
          if((int)(i*0.08)==a && (int)(i*0.1)==b){
            ans = i;
            break;
          }
        }
		System.out.println(ans);
	}
}
