import java.util.*;


public class Main {
	public static void main (String[] args){
		Scanner sc =  new Scanner(System.in);
		float A = sc.nextFloat();
		float B = sc.nextFloat();
		int R = -1;
		float Rmemo = Math.min((float)(A/0.08), (float)(B/0.1));
		while(Rmemo*0.08 < A + 1) {
			int x = (int)Math.floor(Rmemo*0.08);
			int y = (int)Math.floor(Rmemo*0.1);
			if(x == A && y == B) {
				R = (int)Rmemo;
				break;
			}
			Rmemo++;
		}
		System.out.println(R);
	}
} import java.util.*; util.* java public class Main {
	public static void main (String[] args){
		Scanner sc =  new Scanner(System.in);
		float A = sc.nextFloat();
		float B = sc.nextFloat();
		int R = -1;
		float Rmemo = Math.min((float)(A/0.08), (float)(B/0.1));
		while(Rmemo*0.08 < A + 1) {
			int x = (int)Math.floor(Rmemo*0.08);
			int y = (int)Math.floor(Rmemo*0.1);
			if(x == A && y == B) {
				R = (int)Rmemo;
				break;
			}
			Rmemo++;
		}
		System.out.println(R);
	}
} Main public static void main (String[] args){
		Scanner sc =  new Scanner(System.in);
		float A = sc.nextFloat();
		float B = sc.nextFloat();
		int R = -1;
		float Rmemo = Math.min((float)(A/0.08), (float)(B/0.1));
		while(Rmemo*0.08 < A + 1) {
			int x = (int)Math.floor(Rmemo*0.08);
			int y = (int)Math.floor(Rmemo*0.1);
			if(x == A && y == B) {
				R = (int)Rmemo;
				break;
			}
			Rmemo++;
		}
		System.out.println(R);
	} main {
		Scanner sc =  new Scanner(System.in);
		float A = sc.nextFloat();
		float B = sc.nextFloat();
		int R = -1;
		float Rmemo = Math.min((float)(A/0.08), (float)(B/0.1));
		while(Rmemo*0.08 < A + 1) {
			int x = (int)Math.floor(Rmemo*0.08);
			int y = (int)Math.floor(Rmemo*0.1);
			if(x == A && y == B) {
				R = (int)Rmemo;
				break;
			}
			Rmemo++;
		}
		System.out.println(R);
	} Scanner sc =  new Scanner(System.in); sc new Scanner(System.in) float A = sc.nextFloat(); A sc.nextFloat() sc.nextFloat sc float B = sc.nextFloat(); B sc.nextFloat() sc.nextFloat sc int R = -1; R -1 1 float Rmemo = Math.min((float)(A/0.08), (float)(B/0.1)); Rmemo Math.min((float)(A/0.08), (float)(B/0.1)) Math.min Math (float)(A/0.08) A 0.08 (float)(B/0.1) B 0.1 while(Rmemo*0.08 < A + 1) {
			int x = (int)Math.floor(Rmemo*0.08);
			int y = (int)Math.floor(Rmemo*0.1);
			if(x == A && y == B) {
				R = (int)Rmemo;
				break;
			}
			Rmemo++;
		} Rmemo*0.08 < A + 1 Rmemo*0.08 Rmemo 0.08 A + 1 A 1 {
			int x = (int)Math.floor(Rmemo*0.08);
			int y = (int)Math.floor(Rmemo*0.1);
			if(x == A && y == B) {
				R = (int)Rmemo;
				break;
			}
			Rmemo++;
		} int x = (int)Math.floor(Rmemo*0.08); x (int)Math.floor(Rmemo*0.08) Math.floor Math Rmemo*0.08 Rmemo 0.08 int y = (int)Math.floor(Rmemo*0.1); y (int)Math.floor(Rmemo*0.1) Math.floor Math Rmemo*0.1 Rmemo 0.1 if(x == A && y == B) {
				R = (int)Rmemo;
				break;
			} x == A && y == B x == A x A y == B y B {
				R = (int)Rmemo;
				break;
			} R = (int)Rmemo R (int)Rmemo break; Rmemo++ Rmemo System.out.println(R) System.out.println System.out System System.out R String[] args args public class Main {
	public static void main (String[] args){
		Scanner sc =  new Scanner(System.in);
		float A = sc.nextFloat();
		float B = sc.nextFloat();
		int R = -1;
		float Rmemo = Math.min((float)(A/0.08), (float)(B/0.1));
		while(Rmemo*0.08 < A + 1) {
			int x = (int)Math.floor(Rmemo*0.08);
			int y = (int)Math.floor(Rmemo*0.1);
			if(x == A && y == B) {
				R = (int)Rmemo;
				break;
			}
			Rmemo++;
		}
		System.out.println(R);
	}
} public class Main {
	public static void main (String[] args){
		Scanner sc =  new Scanner(System.in);
		float A = sc.nextFloat();
		float B = sc.nextFloat();
		int R = -1;
		float Rmemo = Math.min((float)(A/0.08), (float)(B/0.1));
		while(Rmemo*0.08 < A + 1) {
			int x = (int)Math.floor(Rmemo*0.08);
			int y = (int)Math.floor(Rmemo*0.1);
			if(x == A && y == B) {
				R = (int)Rmemo;
				break;
			}
			Rmemo++;
		}
		System.out.println(R);
	}
} Main
import java.util.*;


public class Main {
	public static void main (String[] args){
		Scanner sc =  new Scanner(System.in);
		float A = sc.nextFloat();
		float B = sc.nextFloat();
		int R = -1;
		float Rmemo = Math.min((float)(A/0.08), (float)(B/0.1));
		while(Rmemo*0.08 < A + 1) {
			int x = (int)Math.floor(Rmemo*0.08);
			int y = (int)Math.floor(Rmemo*0.1);
			if(x == A && y == B) {
				R = (int)Rmemo;
				break;
			}
			Rmemo++;
		}
		System.out.println(R);
	}
}