#include<fstream>
using namespace std;
int i,j,n,p[1000],nr=1;
int main()
{
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	f>>n;
	for(i=3;i<=n;i+=2)
		if(p[i]==0)
			for(j=i*i;j<=n;j=j+i*2)
				p[j]=1;
	for(i=3;i<=n;i+=2)
		if (p[i]==0) 
			nr++;
	g<<nr;
}