#include<iostream>
#include<cmath>

using namespace std;

int isprime(int x){
	int i;
	if(x == 2 || x == 3) return 1;
	else if(x % 2 == 0) return 0;
	else{
		for(i = 3; i <= sqrt(x); i += 2){
			if(x % i == 0) return 0;
		}
		return 1;
	}
}

int main(){
	int n, i, count;
	while(cin >> n){
		count = 0;
		for(i = 2; i <= n; i++){
			if(i % 2 == 0 && isprime(i) == 1) count++;
		}
		cout << count << endl;
	}
	return 0;
}