#include <stdio.h>
#include <fstream>
#include <math.h>
#define lim 2000000
using namespace std;

bool v[lim];

int main() {
	int n, i, j, nr = 1;
	
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	
	in >> n;
	for (i = 3; i <= (int)(sqrt((double)n)); i = i + 2)
		for (j = i * i; j <= n; j = j + i)
			v[i] = true;
	for (i = 3; i <= n; i = i + 2)
		if (v[i] == false)
			nr++;
	out << nr << '\n';

	in.close();
	out.close();
	return 0;
}