#include<fstream>

using namespace std;
#include<iostream>
const int N=2000007;

int eratostene(int n)
{
	bool c[N]={false};
	c[0]=c[1]=true;
	for(int i=2;i*i<=n;++i)
		if(!c[i])
			for (int j=i*i;j<=n;j+=i)
				c[j]=true;
	int nr=0;
	for(int i=0;i<=n;++i)
		if(!c[i])
			++nr;
	return nr;
}

int main()
{
	int n;
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	in>>n;
	out<<eratostene(n);
	return 0;
}