#include <iostream>
#include <fstream>

#define MAX 2000000

using namespace std;

char ciur[MAX];
int count;

void make_ciur(int N){
	for (int i = 2; i <= N; i++)
		if (ciur[i] == 0){
			count++;
			for (int j = i + i; j <= N; j+=i)
				ciur[j] = 1;
		}
}

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

int main() {
	int N;
	f >> N;
	make_ciur(N);
	g << count;
	f.close();
	g.close();
	return 0;
}