#include <fstream>
#include <math.h>
using namespace std;
unsigned char a[2000009];
int main()
{
	unsigned int m,y,i;
	double n;
	ifstream f1("ciur.in");
	f1>>n;
	f1.close();
	m=n;
	for (i=2;i<=n;i++) a[i]=1;
	for (y=2;y<=sqrt(n);y++)
		if (a[y]!=0) 
			for (i=y+y;i<=n;i+=y)
				if (a[i]!=0) 
					{a[i]=0;m--;}
	ofstream f2("ciur.out");
	f2<<m-1;
	f2.close();
	return 0;
}