import java.util.Scanner;

public class Main {
	
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		
		String[] str = s.nextLine().split(" ");
		int n = Integer.parseInt(str[0]);
		int m =Integer.parseInt(str[1]);
		
		if(m>=n){
			System.out.println(1);
					
		}else{
			if(n%m<=m){
				System.out.println(n/m);
			}else {
			
			System.out.println(-1);
			
		}
		
		
	}

}
	
}