#include<iostream>
#include<fstream>
using namespace std;
int prim[2000003];
int N, numar;
int main()
{
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	f>>N;
	int i, j;
	prim[1] = 0;
	for(i=2 ; i <= N ; i++)
	prim[i] = 1;
	for(i=2 ; i <= N ; i++)
		if(prim[i] == 1)
			{numar++;
				for(j=i+i ; j <= N ; j = j+i)
			prim[j] = 0;
			}
	g<<numar;
	return 0;
}