#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

bool a[2000001];
vector <int> V;

int main()
{
    int n;
    f >> n;
    for (int i = 2; i <= n; i++)
    {
        if (a[i] == 0)
        {
            V.push_back(i);
            for (int j = 2*i; j <= n; j += i)
            {
                a[j] = 1;
            }
        }
    }
    g << V.size();
}