#include <bits/stdc++.h>

using namespace std;

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

const int nmax = 2000005;

bitset < nmax > sieve;

int main()
{
    int n;

    fin >> n;

    sieve[0] = sieve[1] = 1;

    for (int i = 4; i <= n; i += 2)
        sieve[i] = 1;

    int sn = sqrt(n), rez = 0;

    for (int i = 3; i <= sn; i += 2)
        if(!sieve[i])
            for (int j = i * i; j <= n; j += 2 * i)
                sieve[j] = 1;


    for (int i = 0; i <= n; i++)
        rez += (sieve[i] == 0);


    fout << rez;


    fin.close();
    fout.close();
    return 0;
}