#include <iostream>
#include <cmath>
#include <fstream>
using namespace std;

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

bool ciur[2000000];

int main() {
	int n, cnt = 0, i;
	fin >> n;

	for (i = 2; i <= n; ++i)
		ciur[i] = true;
	for (i = 2; i <= n; ++i)
		if (ciur[i])
		{
			++cnt;
			for (int j = i + i; j <= n; j += i)
				ciur[j] = 0;
		}
	fout << cnt;
	
	return 0;
}