#include<fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

bool c[2000000];

int main()
{
	int j,i,n,cont=1;
	in>>n;
	for(j=4;j<=n;j=j+2)
		c[j]=true;
	for(i=3;i*i<n;i=i+2)
		if(!c[i])
			for(j=i*i;j<=n;j=j+i)
				c[j]=true;
	for(i=3;i<=n;i++)
		if(!c[i])
			cont++;
	out<<cont;
	return 0;
}