#include <stdio.h>

FILE* f;
FILE* s;

long int i;
long int j;

char sir[2000001];

int main()
{
	f=fopen ("ciur.in","r");
	s=fopen ("ciur.out","w");

	long int n;
	fscanf (f,"%ld",&n);

	long int cnt=0;
	for (i=2;i<=n;i++)
	{
		if (!sir[i])
		{
			cnt++;

			for (j=i+i;j<=n;j+=i)
			{
				sir[j]='1';
			}
	   }
	}

	fprintf (s,"%ld\n",cnt);

	fcloseall();

	return 0;

}