#include<iostream>
#include<fstream>

using namespace std;
int N, cnt;
char prim[2000005];

int main(void)
{
	int i, j;

	ifstream fin("ciur.in");
	ofstream fout("ciur.out");

	fin >> N;
	for (i = 2; i <= N; ++i)
		prim[i] = 1;
	for (i = 2; i <= N; ++i)
	if (prim[i])
	{
		++cnt;
		for (j = i + i; j <= N; j += i)
			prim[j] = 0;
	}

	fout << cnt << endl;

	return 0;
}