#include<fstream>
using namespace std;
const int N=2000001;
int main()
{
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	
	int nr=0,n,i,j,c[N]={0};
	in>>n;
	c[0]=c[1]=1;
	for(j=4;j<=n;j+=2)
		c[j]=1;
	for(i=3;i*i<=n;i+=2)
		if(c[i]==0)
			for(j=i*i;j<=n;j+=i)
				c[j]=1;
	for(i=2;i<=n;++i)
		if(c[i]==0)
		{
			++nr;
			//out<<i<<" ";
		}
	out<<nr;
	in.close();
	out.close();
	return 0;
}