#include <iostream>
#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

bool v[2000001];
int N;
int ct;

int main()
{
	f >> N;
	for(int i = 2; i <= N; i++) {
		v[i] = 1;
	}
	for(int i = 2; i <= N; i++) {
		if(v[i] == 1) {
			ct++;
			for(int j = i + i; j <= N; j += i) {
				v[j] = 0;
			}
		}
	}
	g << ct;
}