import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int a = sc.nextInt();
    	int b = sc.nextInt();
    	int c = sc.nextInt();
    	if (b - a + 1 >= c) {
    	    System.out.println(c);
    	} else {
    	    System.out.println((b % c - (a - 1) % c + c) % c);
    	}
	}
}