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

using namespace std;

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

int n;
bitset<2000001> P;

void Ciur()
{
    P.set();
    P[0] = P[1] = false;
    for (int i = 2; i * i <= n; ++i)
    {
        if (P[i])
        {
            for (int j = i * i; j <= n; j += i)
                P[j] = false;
        }
    }
}

int main()
{
    int cnt = 0;
    fin >> n;
    Ciur();
    for (int i = 1; i <= n; ++i)
    {
        if (P[i])
            ++cnt;
    }
    fout << cnt;

    return 0;
}