import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		// 入力値の取得
		int A = sc.nextInt();
		int B = sc.nextInt();
		
		// 結果の出力
		boolean notFound = true;
		for (int i = 10; i < 1010; i++) {
			if (Math.floor(i * 0.08) == A) {
				if (Math.floor(i * 0.1) == B) {
					System.out.println(i);
					notFound = false;
					break;
				}
				else {
					continue;
				}
			}
			else {
				continue;
			}
		}
		
		if (notFound) {
			System.out.println(-1);
		}

		sc.close();
	}
}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz