1007. 素数对猜想 (20)

import java.util.Scanner;

public class Main {

    public static boolean Isprime(int n){
        boolean flag =true;
        if ( n <= 1 ){
            flag = false;
        }
        else if ( n == 2){
            flag = true;
        }
        else{
            if ( n % 2 == 0 ){
                flag =false;
            }
            else{
                for ( int i = 3 ; i <= Math.sqrt(n) ; i += 2 ){
                    if ( n % i == 0){
                        flag = false;
                        break;
                    }
                }
            }
        }
        return flag;
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int count = 0;
        int[] prime = new int[n];
        for ( int i = 2 ; i <= n ; i++ ){
            if ( Isprime(i) == true ){
                prime[count++] = i;
            }
        }
        int num = 0;
        for ( int i = 0 ; i < count ; i++ ){
            if (prime[i+1] - prime[i] == 2){
                num++;
            }
        }
        System.out.print(num);
        in.close();
    }

}