#include <iostream>
#include <fstream>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
	int N, a[2000000];
	in>>N;
	
	for(int i = 0 ; i<N ; i++)
		a[i]=i+1;
	for(int i = 1 ; i<sqrt(N) ; i++)
		if(a[i] != 0)
			for(int j = a[i] ; j<N ; j = j + i)
				a[j] = 0;
	int count = 0;
	for(int i = 0 ; i<N ; i++)
		if(a[i] != 0) count++;
	out<<count;
	return 0;
}