#include<iostream>
#include<stdio.h>
#include<math.h>

using namespace std;

int v[2000073];

int main()
{
   FILE *f=fopen("ciur.in","r");
   FILE *g=fopen("ciur.out","w");

   int i,n,j,nrp=0;

   fscanf(f,"%d",&n);

  for (i=2;i<=n;i++)
     v[i]=1;

  for (i=2;i<=n;i++)
  {
    if (v[i]==1)
       for (j=i;j<=n/i;j++)
            v[j*i]=0;

  }

  for (i=2;i<=n;i++)
    if (v[i]==1) nrp++;

 fprintf(g,"%d",nrp);




    return 0;
}