#include <fstream>
using namespace std;
bool v[2000002];
long long i,j,n,c;
int main()
{
	ifstream f("ciur.in");
	ofstream q("ciur.out");
	f>>n;
	for (i=2;i<=n;i++)
		v[i]=1;
	for (i=2;i<=n;i++)
		if(v[i]==1)
		{
			c++;
			for(j=i+i;j<=n;j=j+i)
				v[j]=0;
		}
	q<<c;		
	return 0;
}