#include<cstdio>
#define lmax 2000005
using namespace std;
int a[lmax];
bool use[lmax];
int main()
{
	int i,n,l=0,s=0;
	for(i=2;i<lmax;i++)
		if(!use[i])
		{
			a[l++]=i;
			for(int j=i+i;j<lmax;j+=i)
				use[j]=1;
		}
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(i=0;a[i]<=n && a[i];i++)
		s++;
	printf("%d\n",s);
	return 0;
}