#include <bits/stdc++.h>
using namespace std;

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

int n;
bitset<2000001> prim;


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

int main()
{
	int cnt = 0;
	fin >> n;
	ciur(n);
	for (int i = 2; i <= n; i++)
		if (!prim[i])
			cnt++;
	fout << cnt << "\n";
	fin.close();
	fout.close();
	return 0;
}