#include <iostream>
#include <vector>
using namespace std;

int main(){
    vector<int> isprime;
    int n;
    while (cin >> n){
	for (int i = 0; i <= n; i++) isprime.push_back(1);
	
	int prime = 0;
	for (int i = 2; i <= n; i++){
	    if (isprime[i]){
		prime++;
		for (int j = 2; i * j <= n; j++) isprime[i*j] = 0;
	    }
	}
	cout << prime << endl;
	isprime.clear();
    }
    return 0;
}