import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	if (n == 1) {
    	    System.out.println(0);
    	    return;
    	}
    	TreeSet<Integer> primes = new TreeSet<>();
    	for (int i = 2; i <= n; i++) {
    	    if (isPrime(primes, i)) {
    	        primes.add(i);
    	    }
    	}
    	long total = -1;
    	for (int x : primes) {
    	    if (primes.contains(getNum(x + 2))) {
    	        total += 2;
    	    }
    	}
    	System.out.println(total);
    }
    
    static int getNum(int x) {
        int ans = (int)Math.sqrt(x);
        if (ans * ans == x) {
            return ans;
        } else {
            return 0;
        }
    }
    
    static boolean isPrime(TreeSet<Integer> primes, int x) {
        for (int y : primes) {
            if (y * y > x) {
                break;
            }
            if (x % y == 0) {
                return false;
            }
        }
        return true;
    }
    
}