#include <iostream>
#include <fstream>
using namespace std;

short v[2000000];

int main()
{
    int n,i,k,nr=0;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for(i=2;i<=n;i++)
    {
        k=i;
      if(v[i]==0)nr++;
      while(k<=n-i)
      {
          k=k+i;
          v[k]=1;
      }
    }
    g<<nr;
    return 0;
}