import java.util.*;
import java.io.*; 

public class Main {
	
	public static void main(String... string) {
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt(); 
		int y = sc.nextInt();
		for(int i = 0; i<2000; i++) {
			if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				System.out.println(i);
				return; 
			}
		}
		System.out.println(-1); 
	}
} import java.util.*; util.* java import java.io.*; io.* java public class Main {
	
	public static void main(String... string) {
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt(); 
		int y = sc.nextInt();
		for(int i = 0; i<2000; i++) {
			if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				System.out.println(i);
				return; 
			}
		}
		System.out.println(-1); 
	}
} Main public static void main(String... string) {
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt(); 
		int y = sc.nextInt();
		for(int i = 0; i<2000; i++) {
			if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				System.out.println(i);
				return; 
			}
		}
		System.out.println(-1); 
	} main {
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt(); 
		int y = sc.nextInt();
		for(int i = 0; i<2000; i++) {
			if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				System.out.println(i);
				return; 
			}
		}
		System.out.println(-1); 
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int x = sc.nextInt(); x sc.nextInt() sc.nextInt sc int y = sc.nextInt(); y sc.nextInt() sc.nextInt sc for(int i = 0; i<2000; i++) {
			if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				System.out.println(i);
				return; 
			}
		} int i = 0; int i = 0; i 0 i<2000 i 2000 i++ i++ i {
			if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				System.out.println(i);
				return; 
			}
		} {
			if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				System.out.println(i);
				return; 
			}
		} if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				System.out.println(i);
				return; 
			} (int)(i*0.08) == x && (int)(i * 0.1) == y (int)(i*0.08) == x (int)(i*0.08) i 0.08 x (int)(i * 0.1) == y (int)(i * 0.1) i 0.1 y {
				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 1 String... string string public class Main {
	
	public static void main(String... string) {
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt(); 
		int y = sc.nextInt();
		for(int i = 0; i<2000; i++) {
			if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				System.out.println(i);
				return; 
			}
		}
		System.out.println(-1); 
	}
} public class Main {
	
	public static void main(String... string) {
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt(); 
		int y = sc.nextInt();
		for(int i = 0; i<2000; i++) {
			if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				System.out.println(i);
				return; 
			}
		}
		System.out.println(-1); 
	}
} Main
import java.util.*;
import java.io.*; 

public class Main {
	
	public static void main(String... string) {
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt(); 
		int y = sc.nextInt();
		for(int i = 0; i<2000; i++) {
			if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				System.out.println(i);
				return; 
			}
		}
		System.out.println(-1); 
	}
}