#include<iostream.h>
int i,j,n,cn;
bool ok;
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	cin>>n;
	cn=0;
	for(i=2;i<=n;++i)
	{
		ok=1;
		for(j=2;j*j<=i;++j)
		{
			if(i%j==0)
			ok=0;
		}
		if(ok)
		cn++;
	}
	cout<<cn;
	return 0;
}