#include <iostream>
#include <fstream>

using namespace std;

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

bool v[1000001];

int main()
{
    int n;
    in >> n;

    v[0] = 1;
    v[1] = 1;

    for (int i = 2; i * i <= n; i++)
    {
        if (!v[i])
        {
            for (int j = i * i; j <= n; j += i)
                v[j] = 1;
        }
    }

    int c = 0;
    for (int i = 2; i <= n; i++)
        if (!v[i])
            c++;

    out << c;

    return 0;
}