#include <stdio.h>
#include <math.h>
const int N=2000001;
bool prim [N];
int i,k,n;
int main()
{
	for (i=2;i<=N;i++)
		prim [i] = 1;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for (i=2;i<=sqrt(n);i++)
		if(prim[i])
		for (k=i*i;k<=n;k=k+i)
			prim [k] = 0;
	k = 0;	
	for (i=2;i<=n;i++)
		if (prim [i])
			k++;
	printf("%d",k);	
	return 0;
}