#include<stdio.h>
#include<math.h>
int n, i, nrprime, check, j;
int main()

{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	scanf("%d",&n);
	check=1;
	nrprime=0;
	if (n==2) 
		nrprime=1;
	if (n>2)
	{
		nrprime=1;
		for (i=3;i<=n;i=i+2)
		{
			check=1;
			for (j=2;j<=sqrt(i);j++)
				if (i%j==0)
					check=0;
			if (check==1)
		nrprime=nrprime+1;
		}
	}
	printf("%d", nrprime);
	return 0;
}