#include <cstdio>
#include <algorithm>
using namespace std;

bool v[2000005];

int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	int n,nr=0;
	fill(v+1,v+2000005,true);
	scanf("%d",&n);
	for (int i=2;i<=n;i++) v[i]=true;
	for (int i=2;i<=n;i++)
		if (v[i])
		{
			nr++;
			for (int j=i;j<=n;j=j+i)
				v[j]=false;
		}
	printf("%d",nr);
	return 0;
}