#include <iostream>
#include <fstream>

using namespace std;

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

bool ciur[2000005] = {0};

int main()
{

    long k,cnt = 0;
    f>>k;
    for (int i = 2; i <= k; i++)
    {
        if (!ciur[i])
        {
            cnt++;
            for (int j = i * 2; j <= k; j += i)
                ciur[j] = 1;
        }
    }
    g<<cnt;
}