#include<stdio.h>
long nr,n;
char a[2000001];
long sol[1024];
void are()
{
	long i,j;
	for(i=2;i<=n;i++)
		if(!a[i])
			{
			nr++;
			for(j=i+i;j<=n;j+=i)
				a[j]=1;
			}
}
void ana()
{
	freopen("ciur.in","r",stdin);
	scanf("%ld",&n);
}
void mere()
{
	long i,nrp=0;
	freopen("ciur.out","w",stdout);
	printf("%ld\n",nr);

}
int main(void)
{
	ana();are();mere();
	return 0;
}