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