#include<fstream>
#include<cstring>
#include<string.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{
	int n, nr = 0;
	bool* ciur;
	fin >> n;
	ciur = new bool[n + 1];
	memset(ciur, false, sizeof(bool) * (n + 1));
	for (int i = 2; i <= n; i++)
		if (ciur[i] == false)
		{
			nr++;
			for (int j = i * i; j <= n; j += i)
				ciur[j] = true;
		}
	delete[] ciur;
	fout << nr;
}