#include<iostream.h>
#include<fstream.h>

ifstream in("ciur.in");
ofstream out("ciur.out");


int main()
{
    int n,p=0,i,j;
    in>>n;
    bool prim[2000001];
    for (i=2;i<=n;i++)
    prim[i]=true;
    for (i=2;i<=n;i++)
    if (prim[i]==true) 
    {
      for (j=2*i;j<=n;j=j+i)
      prim[j]=false;
      p++;
    }
    
    out<<p;
    return 0;
}