#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,i,k;
int eprim(int n)
{
    int i;
    for(i=2;i<=sqrt(n);i++)
        if(n%i==0||n<=0)return 0;
    return 1;
}
int main()
{
    f>>n;
    for(i=2;i<=n;i+=2)
    {
        if(eprim(i))k++;
        if(i==2)i=1;
    }
    g<<k;
    return 0;
}