#include <iostream>
#include <fstream>
using namespace std;
ifstream f ("ciur.in");
ofstream g ("ciur.out");
long int N,i=3,a=0;
long int prim(long int nr)
{
    int j,ok;
    for (j=2;j<=nr/2;j++)
    if (nr%j==0) return 0;
    return 1;
}
int main()
{
    f>>N;
    for (i=2;i<=N;i++)
    if (prim(i)==1) a++;
    cout<<a;
    return 0;
}