#include<fstream>
const int N=2000001;
using namespace std;
int main()
{
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	int i, n, nr=0,j;
	char 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])
			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;
}