#include <fstream>
#include <bitset>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,ct;
bitset<2000001>ciur;

void Ciur(int x)
{
	ciur[0] = 1;
	ciur[1] = 1;
	for (int i = 4; i <= x; i += 2) ciur[i] = 1;
	for(int i=3; i*i<=x; i+=2)
		if (ciur[i] == 0)
		{
			for (int j = i * i; j <= x; j += 2 * i) ciur[j] = 1;
		}
}
int main()
{
	fin >> n;
	Ciur(n);
	for (int i = 1; i <= n; i++)
		if (ciur[i] == 0)ct++;
	fout << ct;
}