#include<iostream>
#include<fstream>
using namespace std;
int main()
{
	int a[1000000]={0},i,j,y=0,n;
	ifstream in("ciurn.in");
	ofstream out("ciur.out");
	in>>n;
	for(i=2;i*i<=n;i++)
		if(a[i]==0)
			for(j=i*i;j<=n;j=j+i)
				a[j]=1;
	for(i=2;i<=n;i++)
		if(a[i]==0)
			y++;
	out<<y;
	return 0;
}