#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n;
bool neprime[2000005];
int ciur() {
	if (n < 2)return 0;
	for (int i = 3; i * i <= n; i += 2) {
		if (neprime[i] == 0) {
			for (int j = i * i; j <= n; j += i) {
				neprime[j] = 1;
			}
		}
	}
	int prime = 1;
	for (int i = 3; i <= n; i += 2) {
		if (neprime[i] == 0) {
			prime++;
		}
	}
	return prime;
}
int main()
{
	in >> n;
	out<<ciur();
	return 0;
}