#include <stdio.h>
#include <math.h>
long v[10001];
int prim(long x)
{
long prim,j,lim;
	prim=1;
		if((x%2==0 && x!=2) || (x==1) || (x==0))
			return 0;
		else
		   {
			lim=sqrt(x);
			for(j=3;j<=lim;j=j+2)
				if(x%j==0)
				       return 0;
		   }
return 1;
}

int main()
{
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
long x,i,num=0;
scanf("%ld",&x);
for(i=2;i<=x;i++)
      if(prim(i)==1)
	       num++;
printf("%ld\n",num);
return 0;
}