#include <iostream>
#include <fstream>
using namespace std;

int i,j,n,nrprime;
bool a[100];
ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{

    f>>n;
    for (i=1;i<=n;i++)
    a[i]=true;
    for (i=2;i<=n;i++)
        if (a[i]==true){
        nrprime++;
            for (j=i+i;j<=n;j=j+i)
                    a[j]=false;
    }
    g<<nrprime;

    f.close();
    g.close();

}