#include<stdlib.h>
#include<stdio.h>

int main()
{
	int v[100],n,i, nr=0,j;
	FILE *f = fopen("ciur.in" , "rt");
	FILE *g = fopen("ciur.out" , "wt");
	fscanf(f , "%d" , &n);
	for(i=2;i<=n;i++)
	{
		if(v[i]!=-1)
		{
			for(j=2;j<=n/i;j++)
        v[i*j]=-1;
    }
  }
  for(i=2;i<=n;i++)
  {
    if(v[i]==-1)
      nr++;
  }
  fprintf(g, "%d" ,(n-nr-1));
  fclose(f);
  fclose(g);
  return 0;
}