#include<stdio.h>
#define M 20004
char ciur[M];
void main()
{long n,i,k,j;

 FILE *f=fopen("ciur.in","r");
 FILE *g=fopen("ciur.out","W");
 fscanf(f,"%ld", &n);

 k=0;

 ciur[1]=0;

 for(i=1;i<=n;i++)
  if(ciur[i]) {for(j=i+i;j<=n;j=j+i)
		ciur[j]=0;
	       }

 for(i=1;i<=n;i++)
  if(ciur[i]) k++;

 fprintf(g,"%ld",k);

 fclose(f);
 fclose(g);
 }