using namespace std;
#include<stdio.h>
int nr,a[500000],i,j,n;
bool p[2000000];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	nr=1;
	a[nr]=2;
	for(i=3;i<=n;i=i+2)
	{
		if(p[i]==0)
		{
			nr++;
			a[nr]=i;
			for(j=i*i;j<=n;j=j+i);
			{
				p[j]=1;
			}
		}
	}
	printf("%d\n",nr);
	return 0;
}