import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
		int a = scan.nextInt();
		if(a < 0){
			a *= -1;
		}
		int b = scan.nextInt();
		if(b < 0){
			b *= -1;
		}
		System.out.println(a%b);
    }
}