#include <fstream>
#include <vector>

using namespace std;

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

vector < bool > c;

int main()
{
    c.resize(2000001);
    int n, cnt = 0;
    
    cin >> n;
    
    for(int div = 2; div * div <= n; div++)
    {
       if(c[div] == true)
       {
           continue;
       }
       for(int mult = 2 * div; mult <= n; mult += div)
       {
           c[mult] = true;
       }
    }
    
    for(int i = 2; i <= n; i++)
    {
        if(c[i] == 0)
        {
            cnt++;
        }
    }
    
    cout << cnt << '\n';
    return 0;
}