#include <fstream.h>

int main()
{
	long v[200000],n,i,k=0;
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	f>>n;
	v[1]=0;
	v[2]=1;
	for (i=3;i<=n;i=i+2)
		v[i]=1;
	for (i=2;i*i<=n;i++)
		if (v[i]==1)
			for (int j=2;j*i<=n;j++)
				v[j*i]=0;
	
	for (i=2;i<=n;i++)
		if (v[i]==1)
			k++;
	g<<k;
		
	f.close();
	g.close();
	return 0;
	
}