#include<iostream>
#include<fstream>
using namespace std;
bool c[2000005];
int r;
int main()
{
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	int n;
	fin>>n;
	c[0]=c[1]=1;
	for(int i=2;i<=n;++i)
		if(c[i]==0)
		{
			for(int j=2*i;j<=n;j+=i)
				c[j]=1;
			++r;
		}
	fout<<r;
	fin.close();
	fout.close();
	return 0;
}