#include <iostream>
#include <fstream>

using namespace std;

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

int n, cont;
bool ciur[2000001];

void ciuruiala()
{
    for(int i = 2; i*i <= n; i++)
        for(int j = i*i; j <= n; j += i)
            ciur[j] = 1;
}

int main()
{
    in >> n;

    ciuruiala();

    for(int i = 2; i <= n; i++)
        cont += (!ciur[i]);

    out << cont << '\n';

    return 0;
}