#include<fstream>
#include<algorithm>
#define N 2000100
#define FOR(a,b,c) for(register int a=b;a<=c;++a)
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int sol,n;
bool v[N];
int main ()
{
	f>>n;
	FOR(i,2,n)
	if(!v[i])
	{
		for(register int j=2;j*i<=n;++j)
			v[i*j]=1;
		sol++;
	}
	g<<sol;
	return 0;
}
//Look at me!Look at me!The monster inside me has grown this big!