#include <stdio.h>
#include <stdlib.h>
int prim(long n){
	long k;
   for(k=3;k<=n/2;k+=2)
   	if(n%k==0) return 0;
   return 1;
}
int main(){
	FILE *f=fopen("ciur.in","rt");
   long n,nr=1,i;
   fscanf(f,"%ld",&n);
   fclose(f);
   if(n>=3) nr=2;
   for(i=5;i<=n;i+=2)
   	if(prim(i)) nr++;
   f=fopen("ciur.out","wt");
   fprintf(f,"%ld",nr);
   fclose(f);
   return 0;
}