#include<stdio.h>
short int pr[32000];
int main()
{
 long int n,p,np=0,m;
 FILE *f=fopen("ciur.in","r"),*g=fopen("ciur.out","w");
 fscanf(f,"%ld",&n);
 for(p=2;p<=n/2;)
 {
   for(m=2;p*m<=n;m++)
     pr[m*p]=1;
   p++;
   while(pr[p]) p++;
 }
 for(p=2;p<=n;p++)
   if(!pr[p]) np++;
 fprintf(g,"%ld",np);
 return 0;
}