#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
void SieveOfEratosthenes(int n,int cnt=0)
{
	bool prime[n+1];
	memset(prime, true, sizeof(prime));

	for (int p=2; p*p<=n; p++)
	{
		if (prime[p] == true)
		{
			for (int i=p*p; i<=n; i += p)
				prime[i] = false;
		}
	}

	for (int p=2; p<=n; p++)
	if (prime[p])
		cnt++;
   fout<<cnt;
}
int main()
{
     int n;
	fin>>n;
       SieveOfEratosthenes(n);

	return 0;
}