#include "stdio.h"
int viz[2000000];

int eratostene(int n)
{
 int nr=0,i,j;
 for(i=2;i<=n;i++)
  if(viz[i]==0)
  {
   nr++;
   for(j=i*i;j<=n;j+=i)
    viz[j]=1;
  }
 return nr;
}

int main()
{
 FILE *in,*out;
 int n;
 in=fopen("ciur.in","r");
 out=fopen("ciur.out","w");
 fscanf(in,"%d",&n);
 fprintf(out,"%d",eratostene(n));
 fclose(in);
 fclose(out);
 return 0;
}