#include <stdio.h>
#include <math.h>

int prime(long x){
long div,rad;
if(x<=2) return x==2;
if(x%2==0) return 0;
div=3;
rad=sqrt(x);
while(div<=rad)
   if(x%div==0) return 0;
   else div=div+2;
return 1;
}

int main(){
long n,count=0;
FILE *f=fopen("ciur.in","r"),
     *g=fopen("ciur.out","w");
fscanf(f,"%ld",&n);
for(;n>1;n--)
   if(prime(n))  count++; 
fprintf(g,"%ld\n",count);
fclose(g);
return 0;
}