#include <iostream>
#include <fstream>

using namespace std;

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

int main()
{
    int k = 0, n; int a[2000001];
    in >> n;
    for(int i = 2; i <= n; i++)
    {
        if(a[i] == 0)
        {
            k++;
            for(int j = 2 ; j * i <= n; j++) a[j*i] = 1;
        }
    }
    out << k;
    return 0;
}