#include <algorithm>
#include <bitset>
using namespace std;
#define dim 1000000001

//unsigned 
//unsigned char v[dim];
bitset <dim> v;

int main()
{
	long n, f=1;
	freopen ("ciur.in","r",stdin) ;
	freopen ("ciur.out","w",stdout) ;
	
	scanf("%d", &n);
	
	for(int i=2;i<n;++i)
	{
		++i;
		if(!v[i])
		{
			++f;
	        for(int j=i;j<=n/i;++j)
			{
				v[j*i]=1;
				++j;
			}
		}
	}
		printf("%d", f);
		
		return 0;
}