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

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

int ciur(int n)
{
    bool prime[n+1];
    memset(prime, true, sizeof(prime));

    for (int p = 2; p*p <= n; p++)
        if (prime[p])
            for (int i = p*2; i <= n; i += p)
                prime[i] = false;

    int nr = 0;
    for (int p = 2; p <= n; p++)
        if (prime[p])
            nr++;
    return nr;
};

int main()
{

    int n;
    fin >> n;
    fout << ciur(n);

    return 0;
}