# include <stdio.h>      
FILE *f=fopen("ciur.in","r"),*g=fopen("ciur.out","w");   
char P[2000001];
long i,j,d,N;

int main()
{
   fscanf(f,"%ld",&N);
   fclose(f);
   for (i=2;i<=N;i++)
    P[i]=1;
   d=0;
   for (i=2;i<=N;i++)
    if (P[i])
    {
       d++;
       for (j=i+i; j<=N; j+=i)
	P[j] = 0;
    }
    j=1;
    for (i=3;i<=N;i=i+2){
      if (P[i]) j++;
      }
   fprintf(g,"%ld\n", j);
  fclose(g);
  return 0;      
}