#include<fstream>
using namespace std;
ifstream f("ciur.in", ios::in);
ofstream g("ciur.out", ios::out);
int main()
{
    int n,k,i,prim[30],p,j;
    f>>n;
    k=0;
    for(i=2;i<=n;i++)
    prim[i]=1;
    for(i=2;i<=n;i++)
    if(prim[i]==1)
    {
                  k++;
                  for(j=i+i;j<=n;j=j+i)
                  prim[j]=0;}
    g<<k;
    return 0;}