#include <fstream>

using namespace std;

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

void ciur();

bool P[2000005];
int n, nr;

int main()
{
	int i;

	fin >> n;
	ciur();
	fout << nr << '\n';
	return 0;
}

void ciur()
{
	int i, j;

	nr++;
	for (i = 2; i <= n; i += 2)
		P[i] = 1;
	for (i = 3; i <= n;i+=2)
		if (!P[i])
		{
			nr++;
			for (j = i*i; j <= n; j += i)
				P[j] = 1;
		}
}