View Code of Problem 3493

import java.util.*;
public class Main {
	public static void main(String[] args) {
		Scanner in =new Scanner(System.in);
		while(in.hasNext()) {
			int a =in.nextInt();
			int b =in.nextInt();
			if(a==-1 && b==-1) {
				break;
			}
			int count=0;
			for(int i =a;i<=b;i++) {
				if(isPrime(i)) {
					count++;
				}
			}
			System.out.println(count);
		}
	}
	public static boolean isPrime(int n){
		if(n < 2) return false;

		if(n == 2) return true;

		if(n%2==0) return false;

		for(int i = 3; i*i <= n; i += 2) {
			if(n%i == 0) return false;
		}
		return true;
	}
}