#include <iostream>
#include <fstream>
 
using namespace std;
 
ifstream in("ciur.in");
ofstream out("ciur.out");

const int maxDim = 2000001;
int n, nr;
bool a[maxDim];

int main()
{
    in>>n;
	
	for(int i = 2 ; i*i <= n ; i++)
		if(a[i] == false)
			for(int j = i*i ; j <= n ; j += i)
				a[j] = true;
	for(int i = 2 ; i <= n ; i++)
		if(a[i] == false)
			nr++;
	out<<nr;
    return 0;
}