#include <iostream>
#include <vector>

using namespace std;


vector<int> era(int n){
	vector<int> prime;
	bool *is_prime = new bool[n+1];
	fill(is_prime,is_prime+n+1,true);
	is_prime[0] = is_prime[1] = false;
	for(int i = 2; i <= n; i++){
		if(is_prime[i]){
			prime.push_back(i);
			for(int j = i*2; j <= n; j+=i){
				is_prime[j] = false;
			}
		}
	}
	delete []is_prime;
	return prime;
}

int main(){

	int n;
	cin >> n;

	vector<int> p = era(n);
	cout << p.size() << endl;

	return 0;
}