#include <iostream>
#include <fstream>
#include <algorithm>
#include <bitset>

using namespace std;

const int N = 2000000;

bitset <N + 1> ciur;

void CreeazaCiur()
{
    ciur[0] = ciur[1] = 1;
    for (int i = 4; i <= N; i += 2)
        ciur[i] = 1;
    for (int i = 3; i * i <= N; i += 2)
        if (ciur[i] == 0)
            for (int j = i * i; j <= N; j += 2 * i)
                ciur[j] = 1;
}

int main()
{
    CreeazaCiur();
    ifstream fin ("ciur.in");
    int n;
    fin >> n;
    int nrprime = 1;
    for (int i = 3; i <= n; i += 2)
        if (ciur[i] == 0)
            nrprime++;
    ofstream fout ("ciur.out");
    fout << nrprime << '\n';
    return 0;
}