#include <iostream>
#include <fstream>
#include <math.h>
#include <bitset>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
unsigned n;
//nr numerelor prime<=n;
//0==prim
//1=neprim
bitset <2000001>  V;
int main()
{   unsigned i,j,c=0;
    f>>n;
    for(i=2;i<=n;i++)
     {
         if(V[i]==0)
           {
               c++;
               for(j=i;j<=n;j=j+i) V[j]=1;
           }
     }

     g<<c;
    return 0;
}