#include <fstream>
#include <math.h>
using namespace std;

bool notPrime[2000001];

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

int main()
{
    int n, div, cnt_prime = 0, rad;
    fin >> n;
    rad = sqrt(n);
    for (int div = 2; div <= rad; div++)
    {
        if (notPrime[div])
            continue;
        for (int multiple = 2 * div; multiple <= n; multiple += div)
            notPrime[multiple] = true;
    }
    for (int i = 2; i <= n; i++)
    {
        if (notPrime[i] == false)
            cnt_prime++;
    }
    fout << cnt_prime << "\n";
    return 0;
}