#include <fstream>
#include <math.h>
#include <iostream>
using namespace std;
unsigned int a[1000009];
int main()
{
	unsigned int m,y,i;
	double n;
	ifstream f1("c.in");
	f1>>n;
	f1.close();
	m=n;
	for (i=2;i<=n;i++) a[i]=i;
	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("c.out");
	f2<<m-1;
	f2.close();
	return 0;
}