import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
  	int a,b,c=0;
  	a=sc.nextInt();
  	b=sc.nextInt();
  	for(int d=b*10;d<(b+1)*10;d+=1){
  		if((int)(d*0.08)==a){
  			c=d;
  			break;
  		}else{
  			c=-1;
  		}
  	}
  	System.out.print(c);
  }
} import java.util.*; util.* java public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
  	int a,b,c=0;
  	a=sc.nextInt();
  	b=sc.nextInt();
  	for(int d=b*10;d<(b+1)*10;d+=1){
  		if((int)(d*0.08)==a){
  			c=d;
  			break;
  		}else{
  			c=-1;
  		}
  	}
  	System.out.print(c);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
  	int a,b,c=0;
  	a=sc.nextInt();
  	b=sc.nextInt();
  	for(int d=b*10;d<(b+1)*10;d+=1){
  		if((int)(d*0.08)==a){
  			c=d;
  			break;
  		}else{
  			c=-1;
  		}
  	}
  	System.out.print(c);
  } main {
    Scanner sc = new Scanner(System.in);
  	int a,b,c=0;
  	a=sc.nextInt();
  	b=sc.nextInt();
  	for(int d=b*10;d<(b+1)*10;d+=1){
  		if((int)(d*0.08)==a){
  			c=d;
  			break;
  		}else{
  			c=-1;
  		}
  	}
  	System.out.print(c);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a a b b c=0; c 0 a=sc.nextInt() a sc.nextInt() sc.nextInt sc b=sc.nextInt() b sc.nextInt() sc.nextInt sc for(int d=b*10;d<(b+1)*10;d+=1){
  		if((int)(d*0.08)==a){
  			c=d;
  			break;
  		}else{
  			c=-1;
  		}
  	} int d=b*10; int d=b*10; d b*10 b 10 d<(b+1)*10 d (b+1)*10 (b+1) b 1 10 d+=1 d+=1 d 1 {
  		if((int)(d*0.08)==a){
  			c=d;
  			break;
  		}else{
  			c=-1;
  		}
  	} {
  		if((int)(d*0.08)==a){
  			c=d;
  			break;
  		}else{
  			c=-1;
  		}
  	} if((int)(d*0.08)==a){
  			c=d;
  			break;
  		}else{
  			c=-1;
  		} (int)(d*0.08)==a (int)(d*0.08) d 0.08 a {
  			c=d;
  			break;
  		} c=d c d break; {
  			c=-1;
  		} c=-1 c -1 1 System.out.print(c) System.out.print System.out System System.out c String[] args args public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
  	int a,b,c=0;
  	a=sc.nextInt();
  	b=sc.nextInt();
  	for(int d=b*10;d<(b+1)*10;d+=1){
  		if((int)(d*0.08)==a){
  			c=d;
  			break;
  		}else{
  			c=-1;
  		}
  	}
  	System.out.print(c);
  }
} public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
  	int a,b,c=0;
  	a=sc.nextInt();
  	b=sc.nextInt();
  	for(int d=b*10;d<(b+1)*10;d+=1){
  		if((int)(d*0.08)==a){
  			c=d;
  			break;
  		}else{
  			c=-1;
  		}
  	}
  	System.out.print(c);
  }
} Main
import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
  	int a,b,c=0;
  	a=sc.nextInt();
  	b=sc.nextInt();
  	for(int d=b*10;d<(b+1)*10;d+=1){
  		if((int)(d*0.08)==a){
  			c=d;
  			break;
  		}else{
  			c=-1;
  		}
  	}
  	System.out.print(c);
  }
}