#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,nr;
short vc[2000001];
int main()
{
    f>>n;
    for (int i=2; i<=n; i++)
    {
        if (vc[i]==0)
        {
            nr++;
            for (int j=i*2; j<=n; j+=i)
                vc[j]=1;
        }
    }
    g<<nr;
    return 0;
}