#include <iostream>
#include <fstream>

using namespace std;

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

int main()
{
    int n;

    in >> n;

    bool ciur[2000001] = { };

    int cont = 0;

    for(int i = 2; i <= n; i++)
    {
        if(ciur[i] == 0)
        {
            cont++;

            for(int j = i*i; j <= n; j += i)
                ciur[j] = 1;
        }
    }

    out << cont;

    return 0;
}