#include <stdio.h>
#include <stdlib.h>
FILE *in,*out;
int n,i,c[2000001],j,k;
int main()
{  in=fopen("ciur.in","r");
  out=fopen("ciur.out","w");
  fscanf(in,"%d",&n);
  for(i=2;i<=n;i++)
  {
      if(c[j]==0)
      {
          for(j=i*i;j<=n;j++)
          {
              c[j]=1;
          }
      }
  }
  for(i=0;i<=n;i++)
  {
      if(c[i]==0)
      {
          k++;
      }

  }
  fprintf(out,"%d",k);



fclose(in);
fclose(out);

    return 0;
}