#include <iostream>
#include <fstream>

using namespace std;

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

const int NMAX = 2000005;

int n;
bool a[NMAX];

void ciur()
{
    for(int i = 3; i * i <= n; i += 2)
    {
        if(a[i] == false)
        {
            for(int j = i * i; j <= n; j += 2 * i)
            {
                a[j] = true;
            }
        }
    }
    int nrprime = 1;
    for(int i = 3; i <= n; i += 2)
    {
        if(!a[i])
        {
            nrprime++;
        }
    }
    fout << nrprime;
}

int main()
{
    fin >> n;
    ciur();
    return 0;
}