#include <iostream>
using namespace std;

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

int main(){
	int n;
	
	while(cin >> n){
		int a=0;
		for(int i = 1; i <= n; ++i){
			if(prime(i))++a;
	}
		cout << a << '\n';
	}
}