#include <iostream>
#include <fstream>

using namespace std;

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

int v[20001];
void auras(int n)
{
	v[0] = v[1] = 1;
	for(int i = 4; i <= n; i += 2) v[i] = 1;
	for(int i = 3; i * i <= n; i += 2)
	{
		if(v[i] == 0)
		{
			for(int j = i * i; j <= n; j += 2 * i) v[j] = 1;
		}
	}
}

int main()
{
	long long N;
	int nr = 0;
	fin >> N;
	auras(N);
	for(int i = 2; i <= N; i++)
	{
		if(v[i] == 0) nr++;
	}
	fout << nr;
	return 0;
}