import java.util.Scanner;

 
public class Main {
 
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int A = sc.nextInt();
		int B = sc.nextInt();
		
		for(int i = 1; i <= 1250; i++) {
			if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			}
		}
		
		System.out.print(-1);		
		sc.close();
	}
	
} import java.util.Scanner; Scanner java.util public class Main {
 
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int A = sc.nextInt();
		int B = sc.nextInt();
		
		for(int i = 1; i <= 1250; i++) {
			if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			}
		}
		
		System.out.print(-1);		
		sc.close();
	}
	
} Main public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int A = sc.nextInt();
		int B = sc.nextInt();
		
		for(int i = 1; i <= 1250; i++) {
			if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			}
		}
		
		System.out.print(-1);		
		sc.close();
	} main {
		
		Scanner sc = new Scanner(System.in);
		int A = sc.nextInt();
		int B = sc.nextInt();
		
		for(int i = 1; i <= 1250; i++) {
			if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			}
		}
		
		System.out.print(-1);		
		sc.close();
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int A = sc.nextInt(); A sc.nextInt() sc.nextInt sc int B = sc.nextInt(); B sc.nextInt() sc.nextInt sc for(int i = 1; i <= 1250; i++) {
			if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			}
		} int i = 1; int i = 1; i 1 i <= 1250 i 1250 i++ i++ i {
			if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			}
		} {
			if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			}
		} if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			} Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B Math.floor(i * 0.08) == A Math.floor(i * 0.08) Math.floor Math i * 0.08 i 0.08 A Math.floor(i * 0.1) == B Math.floor(i * 0.1) Math.floor Math i * 0.1 i 0.1 B {
				System.out.print(i);	
				sc.close();
				return;
			} System.out.print(i) System.out.print System.out System System.out i sc.close() sc.close sc return; System.out.print(-1) System.out.print System.out System System.out -1 1 sc.close() sc.close sc String[] args args public class Main {
 
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int A = sc.nextInt();
		int B = sc.nextInt();
		
		for(int i = 1; i <= 1250; i++) {
			if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			}
		}
		
		System.out.print(-1);		
		sc.close();
	}
	
} public class Main {
 
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int A = sc.nextInt();
		int B = sc.nextInt();
		
		for(int i = 1; i <= 1250; i++) {
			if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			}
		}
		
		System.out.print(-1);		
		sc.close();
	}
	
} Main
import java.util.Scanner;

 
public class Main {
 
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int A = sc.nextInt();
		int B = sc.nextInt();
		
		for(int i = 1; i <= 1250; i++) {
			if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			}
		}
		
		System.out.print(-1);		
		sc.close();
	}
	
}