#include <iostream>
#include <fstream>
using namespace std;

bool ciur[2000005];
long long n;
void ciurExecute(int k)
{
    for (int i = 2 * k; i <= n; i += k)
        ciur[i] = false;
}

int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");

    in >> n;

    for (int i = 0; i <= n; i++)
        ciur[i] = true;

    int count = 0;
    for (int i = 2; i <= n; i++)
        if (ciur[i])
            count++, ciurExecute(i);

    out << count;

    return 0;
}