#include<fstream>
using namespace std;
bool v[2000002];
int n;
void citire()
{
	ifstream in("ciur.in");
	in>>n;
}
int solve()
{
	int x=0,i,j;
	for (i=2;i<=n/2+1;i++)
	{
		if (!v[i])
			for (j=i+i;j<=n;j+=i)
				v[j]=1;
	}
	for (i=2;i<=n;i++)
		if (v[i]==0)
			x++;
	return x;
}
int main()
{
	citire();
	ofstream out("ciur.out");
	out<<solve();
}